Duplicate dns_db_updatenotify_register registrations need to be
suppressed to ensure that dns_db_updatenotify_unregister is successful.
(cherry picked from commit f13e71e551)
Duplicate dns_db_updatenotify_register registrations need to be
suppressed to ensure that dns_db_updatenotify_unregister is successful.
(cherry picked from commit f13e71e551)