Validate address lookups from ADB

Validate address lookups from ADB

The address lookups from ADB were not being validated, allowing
spoofed responses to be accepted and used for other lookups.

Validate the answers except when CD=1 is set in the triggering
request.  Separate ADB names looked up with CD=1 from those without
CD=1, to prevent the use of unvalidated answers in the normal lookup
case (CD=0).  Set the TTL on unvalidated (pending) responses to
ADB_CACHE_MINIMUM when adding them to the ADB.