lockd: double unregister of inetaddr notifiers

lockd_up() can call lockd_unregister_notifiers twice:
inside lockd_start_svc() when it calls lockd_svc_exit_thread()
and then in error path of lockd_up()

Patch forces lockd_start_svc() to unregister notifiers in all error cases
and removes extra unregister in error path of lockd_up().

Fixes: cb7d224f "lockd: unregister notifier blocks if the service ..."
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Cc: stable@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>