Stop forcing IPv4 and IPv6 traffic on non-SOCKSPorts

After legacy/trac#32994 (moved), the defaults in port_cfg_new() will apply to all parsed ports. (Not just default ports.)

I am not sure what we should do with the extra settings in connection_listener_new():

  if (type != CONN_TYPE_AP_LISTENER) {
    lis_conn->entry_cfg.ipv4_traffic = 1;
    lis_conn->entry_cfg.ipv6_traffic = 1;
    lis_conn->entry_cfg.prefer_ipv6 = 1;
  }

Here are our options:

• leave them there: non-SOCKSPorts will always have IPv4, IPv6, and prefer IPv6 traffic
• copy the defaults from port_cfg_new(): non-SOCKSPorts will always have DNS, Onion, and prefer IPv6 virtual addresses. Forcing these options on might make some configs break.
• delete them: non-SOCKSPorts can now disable IPv4, IPv6, and prefer IPv4 traffic. Some rare configs might break, because they relied on the options being forced on.

Here's what I think we should do long-term:

• set reasonable defaults (in legacy/trac#32994 (moved))
• stop forcing options on (this ticket)
• warn users that some rare configs might break, and they should remove NoIPv4Traffic or NoIPv6Traffic as needed (this changes file)

"prefer IPv6 traffic" was added in legacy/trac#32637 (moved) in 0.4.3.1-alpha. We don't want to force that option on in 0.4.3, that makes the problem worse, and might break some existing configs. See legacy/trac#33608 (moved) for a fix.