net: Convert net_inuse_ops

net_inuse_ops methods expose statistics in /proc.
No one from the rest of pernet_subsys or pernet_device
lists touch net::core::inuse.

So, it's safe to make net_inuse_ops async.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -3112,6 +3112,7 @@ static void __net_exit sock_inuse_exit_net(struct net *net)
 static struct pernet_operations net_inuse_ops = {
 	.init = sock_inuse_init_net,
 	.exit = sock_inuse_exit_net,
+	.async = true,
 };
 
 static __init int net_inuse_init(void)