DNS: respond to AAAA queries with NXDomain

[djs55]

Currently we don't have a working IPv6 stack so clients can't really use the IPv6 addresses they discover. They may cause confusion and possible request timeouts. This is an experiment to see if a network timeout bug is fixed in an IPv6 environment.

Possibly related to [docker/for-mac#1629]

Signed-off-by: David Scott [email protected]