samples: net: dns: Do mDNS query always if mDNS is enabled

If mDNS is enabled, then do the mDNS query always. Earlier we did
the query after we had received response to the normal DNS query.
Also there is no need to print DNS id for mDNS queries as the id
is always 0.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>