This applies only for relays. Previous commit adds two new consensus
parameters that dictate how libevent is configured with DNS resolution.
And so, with a new consensus, we now look at those values in case they
ever change.

Without this, Exit relay would have to HUP or restart to apply any new
Exit DNS consensus parameters.

Related to #40312

Signed-off-by: David Goulet <dgoulet@torproject.org>

It is not called by anything outside of the tests and dns.c.

It hasn't been used since 2009.

This saves about 1% for me on a binary compiled without relay mode.

Closes ticket 33366.

This removes a dependency from the client code on feature/relay.

This is an automated commit, generated by this command:

./scripts/maint/rename_c_identifier.py \
        MIN_DNS_TTL_AT_EXIT MIN_DNS_TTL \
        MAX_DNS_TTL_AT_EXIT MAX_DNS_TTL \
        dns_clip_ttl clip_dns_ttl

I am very glad to have written this script.

This commit won't build yet -- it just puts everything in a slightly
more logical place.

The reasoning here is that "src/core" will hold the stuff that every (or
nearly every) tor instance will need in order to do onion routing.
Other features (including some necessary ones) will live in
"src/feature".  The "src/app" directory will hold the stuff needed
to have Tor be an application you can actually run.

This commit DOES NOT refactor the former contents of src/or into a
logical set of acyclic libraries, or change any code at all.  That
will have to come in the future.

We will continue to move things around and split them in the future,
but I hope this lays a reasonable groundwork for doing so.

The server-side clipping now clamps to one of two values, both
for what to report, and how long to cache.

Additionally, we move some defines to dns.h, and give them better
names.

Because in 95 years, we or our successors will surely care about
enforcing the BSD license terms on this code.  Right?

Also, count ipv6 timeouts vs others.  If we have too many ipv6
requests time out, then we could be degrading performance because of a
broken DNS server that ignores AAAA requests.  Other cases in which
we never learn an AAAA address aren't so bad, since they don't slow
A (ipv4) answers down very much.

In C, we technically aren't supposed to define our own things that
start with an underscore.

This is a purely machine-generated commit.  First, I ran this script
on all the headers in src/{common,or,test,tools/*}/*.h :
==============================

use strict;

my %macros = ();
my %skipped = ();
FILE: for my $fn (@ARGV) {
    my $f = $fn;
    if ($fn !~ /^\.\//) {
	$f = "./$fn";
    }
    $skipped{$fn} = 0;
    open(F, $fn);
    while (<F>) {
	if (/^#ifndef ([A-Za-z0-9_]+)/) {
	    $macros{$fn} = $1;
	    next FILE;
	}
    }
}

print "#!/usr/bin/perl -w -i -p\n\n";
for my $fn (@ARGV) {
    if (! exists $macros{$fn}) {
	print "# No macro known for $fn!\n" if (!$skipped{$fn});
	next;
    }
    if ($macros{$fn} !~ /_H_?$/) {
	print "# Weird macro for $fn...\n";
    }
    my $goodmacro = uc $fn;
    $goodmacro =~ s#.*/##;
    $goodmacro =~ s#[\/\-\.]#_#g;
    print "s/(?<![A-Za-z0-9_])$macros{$fn}(?![A-Za-z0-9_])/TOR_${goodmacro}/g;\n"
}
==============================

It produced the following output, which I then re-ran on those same files:

==============================

s/(?<![A-Za-z0-9_])_TOR_ADDRESS_H(?![A-Za-z0-9_])/TOR_ADDRESS_H/g;
s/(?<![A-Za-z0-9_])_TOR_AES_H(?![A-Za-z0-9_])/TOR_AES_H/g;
s/(?<![A-Za-z0-9_])_TOR_COMPAT_H(?![A-Za-z0-9_])/TOR_COMPAT_H/g;
s/(?<![A-Za-z0-9_])_TOR_COMPAT_LIBEVENT_H(?![A-Za-z0-9_])/TOR_COMPAT_LIBEVENT_H/g;
s/(?<![A-Za-z0-9_])_TOR_CONTAINER_H(?![A-Za-z0-9_])/TOR_CONTAINER_H/g;
s/(?<![A-Za-z0-9_])_TOR_CRYPTO_H(?![A-Za-z0-9_])/TOR_CRYPTO_H/g;
s/(?<![A-Za-z0-9_])TOR_DI_OPS_H(?![A-Za-z0-9_])/TOR_DI_OPS_H/g;
s/(?<![A-Za-z0-9_])_TOR_MEMAREA_H(?![A-Za-z0-9_])/TOR_MEMAREA_H/g;
s/(?<![A-Za-z0-9_])_TOR_MEMPOOL_H(?![A-Za-z0-9_])/TOR_MEMPOOL_H/g;
s/(?<![A-Za-z0-9_])TOR_PROCMON_H(?![A-Za-z0-9_])/TOR_PROCMON_H/g;
s/(?<![A-Za-z0-9_])_TOR_TORGZIP_H(?![A-Za-z0-9_])/TOR_TORGZIP_H/g;
s/(?<![A-Za-z0-9_])_TOR_TORINT_H(?![A-Za-z0-9_])/TOR_TORINT_H/g;
s/(?<![A-Za-z0-9_])_TOR_LOG_H(?![A-Za-z0-9_])/TOR_TORLOG_H/g;
s/(?<![A-Za-z0-9_])_TOR_TORTLS_H(?![A-Za-z0-9_])/TOR_TORTLS_H/g;
s/(?<![A-Za-z0-9_])_TOR_UTIL_H(?![A-Za-z0-9_])/TOR_UTIL_H/g;
s/(?<![A-Za-z0-9_])_TOR_BUFFERS_H(?![A-Za-z0-9_])/TOR_BUFFERS_H/g;
s/(?<![A-Za-z0-9_])_TOR_CHANNEL_H(?![A-Za-z0-9_])/TOR_CHANNEL_H/g;
s/(?<![A-Za-z0-9_])_TOR_CHANNEL_TLS_H(?![A-Za-z0-9_])/TOR_CHANNELTLS_H/g;
s/(?<![A-Za-z0-9_])_TOR_CIRCUITBUILD_H(?![A-Za-z0-9_])/TOR_CIRCUITBUILD_H/g;
s/(?<![A-Za-z0-9_])_TOR_CIRCUITLIST_H(?![A-Za-z0-9_])/TOR_CIRCUITLIST_H/g;
s/(?<![A-Za-z0-9_])_TOR_CIRCUITMUX_EWMA_H(?![A-Za-z0-9_])/TOR_CIRCUITMUX_EWMA_H/g;
s/(?<![A-Za-z0-9_])_TOR_CIRCUITMUX_H(?![A-Za-z0-9_])/TOR_CIRCUITMUX_H/g;
s/(?<![A-Za-z0-9_])_TOR_CIRCUITUSE_H(?![A-Za-z0-9_])/TOR_CIRCUITUSE_H/g;
s/(?<![A-Za-z0-9_])_TOR_COMMAND_H(?![A-Za-z0-9_])/TOR_COMMAND_H/g;
s/(?<![A-Za-z0-9_])_TOR_CONFIG_H(?![A-Za-z0-9_])/TOR_CONFIG_H/g;
s/(?<![A-Za-z0-9_])TOR_CONFPARSE_H(?![A-Za-z0-9_])/TOR_CONFPARSE_H/g;
s/(?<![A-Za-z0-9_])_TOR_CONNECTION_EDGE_H(?![A-Za-z0-9_])/TOR_CONNECTION_EDGE_H/g;
s/(?<![A-Za-z0-9_])_TOR_CONNECTION_H(?![A-Za-z0-9_])/TOR_CONNECTION_H/g;
s/(?<![A-Za-z0-9_])_TOR_CONNECTION_OR_H(?![A-Za-z0-9_])/TOR_CONNECTION_OR_H/g;
s/(?<![A-Za-z0-9_])_TOR_CONTROL_H(?![A-Za-z0-9_])/TOR_CONTROL_H/g;
s/(?<![A-Za-z0-9_])_TOR_CPUWORKER_H(?![A-Za-z0-9_])/TOR_CPUWORKER_H/g;
s/(?<![A-Za-z0-9_])_TOR_DIRECTORY_H(?![A-Za-z0-9_])/TOR_DIRECTORY_H/g;
s/(?<![A-Za-z0-9_])_TOR_DIRSERV_H(?![A-Za-z0-9_])/TOR_DIRSERV_H/g;
s/(?<![A-Za-z0-9_])_TOR_DIRVOTE_H(?![A-Za-z0-9_])/TOR_DIRVOTE_H/g;
s/(?<![A-Za-z0-9_])_TOR_DNS_H(?![A-Za-z0-9_])/TOR_DNS_H/g;
s/(?<![A-Za-z0-9_])_TOR_DNSSERV_H(?![A-Za-z0-9_])/TOR_DNSSERV_H/g;
s/(?<![A-Za-z0-9_])TOR_EVENTDNS_TOR_H(?![A-Za-z0-9_])/TOR_EVENTDNS_TOR_H/g;
s/(?<![A-Za-z0-9_])_TOR_GEOIP_H(?![A-Za-z0-9_])/TOR_GEOIP_H/g;
s/(?<![A-Za-z0-9_])_TOR_HIBERNATE_H(?![A-Za-z0-9_])/TOR_HIBERNATE_H/g;
s/(?<![A-Za-z0-9_])_TOR_MAIN_H(?![A-Za-z0-9_])/TOR_MAIN_H/g;
s/(?<![A-Za-z0-9_])_TOR_MICRODESC_H(?![A-Za-z0-9_])/TOR_MICRODESC_H/g;
s/(?<![A-Za-z0-9_])_TOR_NETWORKSTATUS_H(?![A-Za-z0-9_])/TOR_NETWORKSTATUS_H/g;
s/(?<![A-Za-z0-9_])_TOR_NODELIST_H(?![A-Za-z0-9_])/TOR_NODELIST_H/g;
s/(?<![A-Za-z0-9_])_TOR_NTMAIN_H(?![A-Za-z0-9_])/TOR_NTMAIN_H/g;
s/(?<![A-Za-z0-9_])_TOR_ONION_H(?![A-Za-z0-9_])/TOR_ONION_H/g;
s/(?<![A-Za-z0-9_])_TOR_OR_H(?![A-Za-z0-9_])/TOR_OR_H/g;
s/(?<![A-Za-z0-9_])_TOR_POLICIES_H(?![A-Za-z0-9_])/TOR_POLICIES_H/g;
s/(?<![A-Za-z0-9_])_TOR_REASONS_H(?![A-Za-z0-9_])/TOR_REASONS_H/g;
s/(?<![A-Za-z0-9_])_TOR_RELAY_H(?![A-Za-z0-9_])/TOR_RELAY_H/g;
s/(?<![A-Za-z0-9_])_TOR_RENDCLIENT_H(?![A-Za-z0-9_])/TOR_RENDCLIENT_H/g;
s/(?<![A-Za-z0-9_])_TOR_RENDCOMMON_H(?![A-Za-z0-9_])/TOR_RENDCOMMON_H/g;
s/(?<![A-Za-z0-9_])_TOR_RENDMID_H(?![A-Za-z0-9_])/TOR_RENDMID_H/g;
s/(?<![A-Za-z0-9_])_TOR_RENDSERVICE_H(?![A-Za-z0-9_])/TOR_RENDSERVICE_H/g;
s/(?<![A-Za-z0-9_])_TOR_REPHIST_H(?![A-Za-z0-9_])/TOR_REPHIST_H/g;
s/(?<![A-Za-z0-9_])_TOR_REPLAYCACHE_H(?![A-Za-z0-9_])/TOR_REPLAYCACHE_H/g;
s/(?<![A-Za-z0-9_])_TOR_ROUTER_H(?![A-Za-z0-9_])/TOR_ROUTER_H/g;
s/(?<![A-Za-z0-9_])_TOR_ROUTERLIST_H(?![A-Za-z0-9_])/TOR_ROUTERLIST_H/g;
s/(?<![A-Za-z0-9_])_TOR_ROUTERPARSE_H(?![A-Za-z0-9_])/TOR_ROUTERPARSE_H/g;
s/(?<![A-Za-z0-9_])TOR_ROUTERSET_H(?![A-Za-z0-9_])/TOR_ROUTERSET_H/g;
s/(?<![A-Za-z0-9_])TOR_STATEFILE_H(?![A-Za-z0-9_])/TOR_STATEFILE_H/g;
s/(?<![A-Za-z0-9_])_TOR_STATUS_H(?![A-Za-z0-9_])/TOR_STATUS_H/g;
s/(?<![A-Za-z0-9_])TOR_TRANSPORTS_H(?![A-Za-z0-9_])/TOR_TRANSPORTS_H/g;
s/(?<![A-Za-z0-9_])_TOR_TEST_H(?![A-Za-z0-9_])/TOR_TEST_H/g;
s/(?<![A-Za-z0-9_])_TOR_FW_HELPER_H(?![A-Za-z0-9_])/TOR_TOR_FW_HELPER_H/g;
s/(?<![A-Za-z0-9_])_TOR_FW_HELPER_NATPMP_H(?![A-Za-z0-9_])/TOR_TOR_FW_HELPER_NATPMP_H/g;
s/(?<![A-Za-z0-9_])_TOR_FW_HELPER_UPNP_H(?![A-Za-z0-9_])/TOR_TOR_FW_HELPER_UPNP_H/g;
==============================