resolve/mdns: do not append goodby packet entries to known answers section

resolve/mdns: do not append goodby packet entries to known answers section

When we receive a goodby packet about a host, and we have a cache entry about
the host, we do not immediately remove the cache entry, but update it with TTL 1.
See RFC 6762 section 10.1 and 3755027c2cada70345c96787a9b5569994dd23ed.

If we receive a request soon after the goodby packet, previously the
entry was included in the known answers section of the reply. But such
information should not be appended.

Follow-up for 3755027c2cada70345c96787a9b5569994dd23ed.