Don't use _services._dns-sd._tcp.local

It seems mdns(d) was trying to support queries for two records with
following names:
1) _services._dns-sd._udp.local
2) _services._dns-sd._tcp.local

According to the RFC 6763 Section 9 only the first one should be used
and response PTR records should include services of both protocols: UDP
and TCP.

This fixes discovering TCP services as in practice no other software was
sending queries with _services._dns-sd._tcp.local.

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