resolved: skip conflict notifications for DNS-SD PTR RRs

Enumerating DNS-SD PTR resource records are a special case and
are supposed to have non-unique keys pointing to services of the
same type running on different hosts. There's no need for them
to be checked for conflicts.

Thus don't check for conflicts such RRs.

src/resolve/resolved-dns-scope.c

@@ -991,6 +991,10 @@ void dns_scope_check_conflicts(DnsScope *scope, DnsPacket *p) {
 
         for (i = 0; i < p->answer->n_rrs; i++) {
 
+                /* No conflict if it is DNS-SD RR used for service enumeration. */
+                if (dns_resource_key_is_dnssd_ptr(p->answer->items[i].rr->key))
+                        continue;
+
                 /* Check for conflicts against the local zone. If we
                  * found one, we won't check any further */
                 r = dns_zone_check_conflicts(&scope->zone, p->answer->items[i].rr);