net: Convert pernet_subsys ops, registered via net_dev_init()

There are:
1)dev_proc_ops and dev_mc_net_ops, which create and destroy
pernet proc file and not interesting for another net namespaces;
2)netdev_net_ops, which creates pernet hashes, which are not
touched by another pernet_operations.

So, make them 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/dev.c

@@ -8833,6 +8833,7 @@ static void __net_exit netdev_exit(struct net *net)
 static struct pernet_operations __net_initdata netdev_net_ops = {
 	.init = netdev_init,
 	.exit = netdev_exit,
+	.async = true,
 };
 
 static void __net_exit default_device_exit(struct net *net)