net: Convert ipvs_core_dev_ops

Exit method stops two per-net threads and cancels
delayed work. Everything looks nicely per-net divided.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netfilter/ipvs/ip_vs_core.c

@@ -2294,6 +2294,7 @@ static struct pernet_operations ipvs_core_ops = {
 
 static struct pernet_operations ipvs_core_dev_ops = {
 	.exit = __ip_vs_dev_cleanup,
+	.async = true,
 };
 
 /*