net: Convert vxlan_net_ops

These pernet_operations are similar to bond_net_ops. Exit method
unregisters all net vlanx devices, and it looks like another
pernet_operations are not interested in foreign net vlanx list.
So, it's possible to mark them async.
Signed-off-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -3752,6 +3752,7 @@ static struct pernet_operations vxlan_net_ops = {
 	.exit_batch = vxlan_exit_batch_net,
 	.id   = &vxlan_net_id,
 	.size = sizeof(struct vxlan_net),
+	.async = true,
 };
 
 static int __init vxlan_init_module(void)