net: Convert brnf_net_ops

These pernet_operations only unregister nf hooks.
So, they are able to be marked as async.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_netfilter_hooks.c

@@ -967,6 +967,7 @@ static struct pernet_operations brnf_net_ops __read_mostly = {
 	.exit = brnf_exit_net,
 	.id   = &brnf_net_id,
 	.size = sizeof(struct brnf_net),
+	.async = true,
 };
 
 static struct notifier_block brnf_notifier __read_mostly = {