net: Convert smack_net_ops

These pernet_operations only register and 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>

security/smack/smack_netfilter.c

@@ -89,6 +89,7 @@ static void __net_exit smack_nf_unregister(struct net *net)
 static struct pernet_operations smack_net_ops = {
 	.init = smack_nf_register,
 	.exit = smack_nf_unregister,
+	.async = true,
 };
 
 static int __init smack_nf_ip_init(void)