net: Convert packet_net_ops

These pernet_operations just create and destroy /proc entry,
and another operations do not touch it.

Also, nobody else are interested in foreign net::packet::sklist.

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/packet/af_packet.c

@@ -4557,6 +4557,7 @@ static void __net_exit packet_net_exit(struct net *net)
 static struct pernet_operations packet_net_ops = {
 	.init = packet_net_init,
 	.exit = packet_net_exit,
+	.async = true,
 };