Keep the live-internet test instances on the standard DNS port

Keep the live-internet test instances on the standard DNS port

The ns1 instances in mirror_root_zone and rfc5011 talk to the root
servers on the live internet: the options-level port must remain 53
for outgoing queries to reach the real servers, and the *-source
addresses must remain unset so that a routable source address is
picked. Exempt these two configs from the standard plumbing and
spell out the intent in a comment.

Assisted-by: Claude:claude-fable-5