Don't call dns_reply_a from service_reply

Don't call dns_reply_a from service_reply

This simplifies code without changing any behavior. Having this call in
service_reply required checking two conditions and was making code flow
harder to follow.

There are 2 more service_reply calls in the project:
1) In service_announce_services where we iterate over &services and
   every element of this list has "service" field filled. It means match
   argument was never NULL and dns_reply_a was never called from there.
2) In parse_question which also receives some name (there is a proper
   check in the dns_handle_packet). No call there neither.

So after all there was only 1 place that was indeed calling dns_reply_a.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: John Crispin <john@phrozen.org>