Fix a data race between the dns_zone and dns_catz modules

Fix a data race between the dns_zone and dns_catz modules

The dns_zone_catz_enable_db() and dns_zone_catz_disable_db()
functions can race with similar operations in the catz module
because there is no synchronization between the threads.

Add catz functions which use the view's catalog zones' lock
when registering/unregistering the database update notify callback,
and use those functions in the dns_zone module, instead of doing it
directly.