macvlan: fix failure during registration v3

If macvlan_common_newlink fails in register_netdevice after macvlan_init
then it decrements port->count twice, first in macvlan_uninit (from
register_netdevice or rollback_registered) and then again in
macvlan_common_newlink.
A similar problem may exist in the ipvlan driver.
This patch consolidates modifications to port->count into macvlan_init
and macvlan_uninit (thanks to Eric Biederman for suggesting this approach).

v3: remove macvtap specific bits.

Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macvlan.c

@@ -795,6 +795,7 @@ static int macvlan_init(struct net_device *dev)
 {
 	struct macvlan_dev *vlan = netdev_priv(dev);
 	const struct net_device *lowerdev = vlan->lowerdev;
+	struct macvlan_port *port = vlan->port;
 
 	dev->state		= (dev->state & ~MACVLAN_STATE_MASK) |
 				  (lowerdev->state & MACVLAN_STATE_MASK);
@@ -812,6 +813,8 @@ static int macvlan_init(struct net_device *dev)
 	if (!vlan->pcpu_stats)
 		return -ENOMEM;
 
+	port->count += 1;
+
 	return 0;
 }
 
@@ -1312,10 +1315,9 @@ int macvlan_common_newlink(struct net *src_net, struct net_device *dev,
 			return err;
 	}
 
-	port->count += 1;
 	err = register_netdevice(dev);
 	if (err < 0)
-		goto destroy_port;
+		return err;
 
 	dev->priv_flags |= IFF_MACVLAN;
 	err = netdev_upper_dev_link(lowerdev, dev);
@@ -1330,10 +1332,6 @@ int macvlan_common_newlink(struct net *src_net, struct net_device *dev,
 
 unregister_netdev:
 	unregister_netdevice(dev);
-destroy_port:
-	port->count -= 1;
-	if (!port->count)
-		macvlan_port_destroy(lowerdev);
 
 	return err;
 }