xfrm: remove the unnecessary .net_exit for xfrmi

The xfrm_if(s) on each netns can be deleted when its xfrmi dev is
deleted. xfrmi dev's removal can happen when:

  a. netns is being removed and all xfrmi devs will be deleted.

  b. rtnl_link_unregister(&xfrmi_link_ops) in xfrmi_fini() when
     xfrm_interface.ko is being unloaded.

So there's no need to use xfrmi_exit_net() to clean any xfrm_if up.

v1->v2:
  - Fix some changelog.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_interface.c

@@ -732,30 +732,7 @@ static struct rtnl_link_ops xfrmi_link_ops __read_mostly = {
 	.get_link_net	= xfrmi_get_link_net,
 };
 
-static void __net_exit xfrmi_destroy_interfaces(struct xfrmi_net *xfrmn)
-{
-	struct xfrm_if *xi;
-	LIST_HEAD(list);
-
-	xi = rtnl_dereference(xfrmn->xfrmi[0]);
-	if (!xi)
-		return;
-
-	unregister_netdevice_queue(xi->dev, &list);
-	unregister_netdevice_many(&list);
-}
-
-static void __net_exit xfrmi_exit_net(struct net *net)
-{
-	struct xfrmi_net *xfrmn = net_generic(net, xfrmi_net_id);
-
-	rtnl_lock();
-	xfrmi_destroy_interfaces(xfrmn);
-	rtnl_unlock();
-}
-
 static struct pernet_operations xfrmi_net_ops = {
-	.exit = xfrmi_exit_net,
 	.id   = &xfrmi_net_id,
 	.size = sizeof(struct xfrmi_net),
 };