net: Convert mpls_net_ops

These pernet_operations register and unregister sysctl table.
Exit methods frees platform_labels from net::mpls::platform_label.
Everything is per-net, and they looks safe to be marked async.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mpls/af_mpls.c

@@ -2488,6 +2488,7 @@ static void mpls_net_exit(struct net *net)
 static struct pernet_operations mpls_net_ops = {
 	.init = mpls_net_init,
 	.exit = mpls_net_exit,
+	.async = true,
 };
 
 static struct rtnl_af_ops mpls_af_ops __read_mostly = {