ipvlan: Fix failure path in dev registration during link creation

When newlink creation fails at device-registration, the port->count
is decremented twice. Francesco Ruggeri (fruggeri@arista.com) found
this issue in Macvlan and the same exists in IPvlan driver too.

While fixing this issue I noticed another issue of missing unregister
in case of failure, so adding it to the fix which is similar to the
macvlan fix by Francesco in commit 30837960 ("macvlan: fix failure
during registration v3")
Reported-by: NFrancesco Ruggeri <fruggeri@arista.com>
Signed-off-by: NMahesh Bandewar <maheshb@google.com>
CC: Eric Dumazet <edumazet@google.com>
CC: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ipvlan/ipvlan_main.c

@@ -113,6 +113,7 @@ static int ipvlan_init(struct net_device *dev)
 {
 	struct ipvl_dev *ipvlan = netdev_priv(dev);
 	const struct net_device *phy_dev = ipvlan->phy_dev;
+	struct ipvl_port *port = ipvlan->port;
 
 	dev->state = (dev->state & ~IPVLAN_STATE_MASK) |
 		     (phy_dev->state & IPVLAN_STATE_MASK);
@@ -128,6 +129,8 @@ static int ipvlan_init(struct net_device *dev)
 	if (!ipvlan->pcpu_stats)
 		return -ENOMEM;
 
+	port->count += 1;
+
 	return 0;
 }
 
@@ -481,27 +484,21 @@ static int ipvlan_link_new(struct net *src_net, struct net_device *dev,
 
 	dev->priv_flags |= IFF_IPVLAN_SLAVE;
 
-	port->count += 1;
 	err = register_netdevice(dev);
 	if (err < 0)
-		goto ipvlan_destroy_port;
+		return err;
 
 	err = netdev_upper_dev_link(phy_dev, dev);
-	if (err)
-		goto ipvlan_destroy_port;
+	if (err) {
+		unregister_netdevice(dev);
+		return err;
+	}
 
 	list_add_tail_rcu(&ipvlan->pnode, &port->ipvlans);
 	ipvlan_set_port_mode(port, mode);
 
 	netif_stacked_transfer_operstate(phy_dev, dev);
 	return 0;
-
-ipvlan_destroy_port:
-	port->count -= 1;
-	if (!port->count)
-		ipvlan_port_destroy(phy_dev);
-
-	return err;
 }
 
 static void ipvlan_link_delete(struct net_device *dev, struct list_head *head)