net: Convert iptable_mangle_net_ops

These pernet_operations unregister net::ipv4::iptable_mangle table.
Another net/pernet_operations do not send ipv4 packets to foreign
net namespaces. So, we mark them async.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/netfilter/iptable_mangle.c

@@ -113,6 +113,7 @@ static void __net_exit iptable_mangle_net_exit(struct net *net)
 
 static struct pernet_operations iptable_mangle_net_ops = {
 	.exit = iptable_mangle_net_exit,
+	.async = true,
 };
 
 static int __init iptable_mangle_init(void)