bridge: Reintroduce log message that was lost (and wrong).

Setting the 'mac' in the Interface record for a bridge's local port has
always been ineffective, but the log message was suppressed because of a
check at too high of a level.  This commit fixes the problem.  It also
fixes the wording of the log message, which has been obsolete since the
introduction of the database.

Finally, it seems better to check for the local port before checking for a
multicast address, so this reverses the order of the checks.