netdev: change name dropping error codes

If changename notifier returns an error code, it gets incorrectly
cleared during rollback so the error is never returned to the user.
Found while testing similar code for MTU changes.
Signed-off-by: NStephen Hemminger <shemminger@vyatta.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -924,10 +924,10 @@ int dev_change_name(struct net_device *dev, const char *newname)
 		strlcpy(dev->name, newname, IFNAMSIZ);
 
 rollback:
-	err = device_rename(&dev->dev, dev->name);
-	if (err) {
+	ret = device_rename(&dev->dev, dev->name);
+	if (ret) {
 		memcpy(dev->name, oldname, IFNAMSIZ);
-		return err;
+		return ret;
 	}
 
 	write_lock_bh(&dev_base_lock);