net: Convert rds_tcp_net_ops

These pernet_operations create and destroy sysctl table
and listen socket. Also, exit method flushes global
workqueue and work. Everything looks per-net safe,
so we can mark them async.
Signed-off-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/rds/tcp.c

@@ -515,6 +515,7 @@ static struct pernet_operations rds_tcp_net_ops = {
 	.exit = rds_tcp_exit_net,
 	.id = &rds_tcp_netid,
 	.size = sizeof(struct rds_tcp_net),
+	.async = true,
 };
 
 static void rds_tcp_kill_sock(struct net *net)