dev: set iflink to 0 for virtual interfaces

Virtual interfaces are supposed to set an iflink value != of their ifindex.
It was not the case for some of them, like vxlan, bond or bridge.
Let's set iflink to 0 when dev->rtnl_link_ops is set.
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -672,6 +672,10 @@ int dev_get_iflink(const struct net_device *dev)
 	if (dev->netdev_ops && dev->netdev_ops->ndo_get_iflink)
 		return dev->netdev_ops->ndo_get_iflink(dev);
 
+	/* If dev->rtnl_link_ops is set, it's a virtual interface. */
+	if (dev->rtnl_link_ops)
+		return 0;
+
 	return dev->ifindex;
 }
 EXPORT_SYMBOL(dev_get_iflink);