Return empty response and NOERROR for AAAA record queries
for DNS names for which we have an A record.
This is to allow for callers that might be first sending an AAAA query and then,
if that does not return a response, follow with an A record query.
Previously we were returning NOTIMPL that caused some callers
to potentially not follow with an A record query or misbehave in different ways.
Also return NXDOMAIN for AAAA record queries for names
that we DO NOT have an A record for to ensure that the callers
do not follow up with an A record query.
Returning an empty response and NOERROR is the behaviour
that RFC 4074 recommends:
https://datatracker.ietf.org/doc/html/rfc4074
Updates tailscale/tailscale#12321
Signed-off-by: Irbe Krumina <irbe@tailscale.com>
6f2bae019f