vlan: unlink the upper neighbour before unregistering

On netdev unregister we're removing also all of its sysfs-associated stuff,
including the sysfs symlinks that are controlled by netdev neighbour code.
Also, it's a subtle race condition - cause we can still access it after
unregistering.

Move the unlinking right before the unregistering to fix both.

CC: Patrick McHardy <kaber@trash.net>
CC: "David S. Miller" <davem@davemloft.net>
Signed-off-by: NVeaceslav Falico <vfalico@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/8021q/vlan.c

@@ -98,14 +98,14 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)
 		vlan_gvrp_request_leave(dev);
 
 	vlan_group_set_device(grp, vlan->vlan_proto, vlan_id, NULL);
+
+	netdev_upper_dev_unlink(real_dev, dev);
 	/* Because unregister_netdevice_queue() makes sure at least one rcu
 	 * grace period is respected before device freeing,
 	 * we dont need to call synchronize_net() here.
 	 */
 	unregister_netdevice_queue(dev, head);
 
-	netdev_upper_dev_unlink(real_dev, dev);
-
 	if (grp->nr_vlan_devs == 0) {
 		vlan_mvrp_uninit_applicant(real_dev);
 		vlan_gvrp_uninit_applicant(real_dev);