relay: Simplify IPv6 discovery when building descriptor

Now that relay_find_addr_to_publish() checks if we actually have an ORPort, we
can simplify the descriptor building phase for IPv6.

This also avoid triggering an IPv6 discovery if the IPv4 can't be found in the
first place.

Related to #40254

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

src/feature/relay/router.c

@@ -2047,12 +2047,11 @@ MOCK_IMPL(STATIC int,
 router_build_fresh_unsigned_routerinfo,(routerinfo_t **ri_out))
 {
   routerinfo_t *ri = NULL;
-  tor_addr_t ipv4_addr, ipv6_addr;
+  tor_addr_t ipv4_addr;
   char platform[256];
   int hibernating = we_are_hibernating();
   const or_options_t *options = get_options();
   int result = TOR_ROUTERINFO_ERROR_INTERNAL_BUG;
-  uint16_t ipv6_orport = 0;
 
   if (BUG(!ri_out)) {
     result = TOR_ROUTERINFO_ERROR_INTERNAL_BUG;
@@ -2064,10 +2063,6 @@ router_build_fresh_unsigned_routerinfo,(routerinfo_t **ri_out))
   bool have_v4 = relay_find_addr_to_publish(options, AF_INET,
                                             RELAY_FIND_ADDR_NO_FLAG,
                                             &ipv4_addr);
-  bool have_v6 = relay_find_addr_to_publish(options, AF_INET6,
-                                            RELAY_FIND_ADDR_NO_FLAG,
-                                            &ipv6_addr);
-
   /* Tor requires a relay to have an IPv4 so bail if we can't find it. */
   if (!have_v4) {
     log_info(LD_CONFIG, "Don't know my address while generating descriptor. "
@@ -2079,24 +2074,21 @@ router_build_fresh_unsigned_routerinfo,(routerinfo_t **ri_out))
   /* Log a message if the address in the descriptor doesn't match the ORPort
    * and DirPort addresses configured by the operator. */
   router_check_descriptor_address_consistency(&ipv4_addr);
-  router_check_descriptor_address_consistency(&ipv6_addr);
 
   ri = tor_malloc_zero(sizeof(routerinfo_t));
+  tor_addr_copy(&ri->ipv4_addr, &ipv4_addr);
   ri->cache_info.routerlist_index = -1;
   ri->nickname = tor_strdup(options->Nickname);
 
   /* IPv4. */
-  tor_addr_copy(&ri->ipv4_addr, &ipv4_addr);
   ri->ipv4_orport = routerconf_find_or_port(options, AF_INET);
   ri->ipv4_dirport = routerconf_find_dir_port(options, 0);
 
-  /* IPv6. Do not publish an IPv6 if we don't have an ORPort that can be used
-   * with the address. This is possible for instance if the ORPort is
-   * IPv4Only. */
-  ipv6_orport = routerconf_find_or_port(options, AF_INET6);
-  if (have_v6 && ipv6_orport != 0) {
-    tor_addr_copy(&ri->ipv6_addr, &ipv6_addr);
-    ri->ipv6_orport = ipv6_orport;
+  /* Optionally check for an IPv6. We still publish without one. */
+  if (relay_find_addr_to_publish(options, AF_INET6, RELAY_FIND_ADDR_NO_FLAG,
+                                 &ri->ipv6_addr)) {
+    ri->ipv6_orport = routerconf_find_or_port(options, AF_INET6);
+    router_check_descriptor_address_consistency(&ri->ipv6_addr);
   }
 
   ri->supports_tunnelled_dir_requests =