net: Convet ipv6_net_ops

These pernet_operations are similar to ipv4_net_ops.
They are safe to be async.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c

@@ -401,6 +401,7 @@ static struct pernet_operations ipv6_net_ops = {
 	.exit = ipv6_net_exit,
 	.id = &conntrack6_net_id,
 	.size = sizeof(struct conntrack6_net),
+	.async = true,
 };
 
 static int __init nf_conntrack_l3proto_ipv6_init(void)