net: Simplfy default_device_exit and improve batching.

- Defer dellink to net_cleanup() allowing for batching.
- Fix comment.
- Use for_each_netdev_safe again as dev_change_net_namespace touches
  at most one network device (unlike veth dellink).
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -5736,14 +5736,13 @@ static struct pernet_operations __net_initdata netdev_net_ops = {
 
 static void __net_exit default_device_exit(struct net *net)
 {
-	struct net_device *dev;
+	struct net_device *dev, *aux;
 	/*
-	 * Push all migratable of the network devices back to the
+	 * Push all migratable network devices back to the
 	 * initial network namespace
 	 */
 	rtnl_lock();
-restart:
-	for_each_netdev(net, dev) {
+	for_each_netdev_safe(net, dev, aux) {
 		int err;
 		char fb_name[IFNAMSIZ];
 
@@ -5751,11 +5750,9 @@ static void __net_exit default_device_exit(struct net *net)
 		if (dev->features & NETIF_F_NETNS_LOCAL)
 			continue;
 
-		/* Delete virtual devices */
-		if (dev->rtnl_link_ops && dev->rtnl_link_ops->dellink) {
-			dev->rtnl_link_ops->dellink(dev, NULL);
-			goto restart;
-		}
+		/* Leave virtual devices for the generic cleanup */
+		if (dev->rtnl_link_ops)
+			continue;
 
 		/* Push remaing network devices to init_net */
 		snprintf(fb_name, IFNAMSIZ, "dev%d", dev->ifindex);
@@ -5765,7 +5762,6 @@ static void __net_exit default_device_exit(struct net *net)
 				__func__, dev->name, err);
 			BUG();
 		}
-		goto restart;
 	}
 	rtnl_unlock();
 }