When dns_request_create() failed in notify_send_toaddr(), sending the
notify would silently fail. When notify_done() failed, the error would
be logged on the DEBUG(2) level.
This commit remedies the situation by:
* Promoting several messages related to notifies to INFO level and add
a "success" log message at the INFO level
* Adding a TCP fallback - when sending the notify over UDP fails, named
will retry sending notify over TCP and log the information on the
NOTICE level
* When sending the notify over TCP fails, it will be logged on the
WARNING level
Closes: #4001, #4002
0d48ac5a93