net: Convert iptable_nat_net_ops

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

net/ipv4/netfilter/iptable_nat.c

@@ -129,6 +129,7 @@ static void __net_exit iptable_nat_net_exit(struct net *net)
 
 static struct pernet_operations iptable_nat_net_ops = {
 	.exit	= iptable_nat_net_exit,
+	.async	= true,
 };
 
 static int __init iptable_nat_init(void)