Synthesize an SOA record for the zone, return it for direct SOA
queries, and include it in the authority section of empty responses
so resolvers can negative-cache properly. RCODE stays NOERROR rather
than NXDOMAIN, since mDNS can't reliably prove non-existence.
Enable dual-stack mDNS lookups (Zeroconf ip_version was set to a value
that matched no IPVersion member), add AAAA query handling, and include
AAAA glue records for SRV targets. Link-local IPv6/IPv4 addresses are
filtered out since they aren't usable by clients off the local link.
franck