rtnetlink: provide permanent hardware address in RTM_NEWLINK

Permanent hardware address of a network device was traditionally provided via ethtool ioctl interface but as Jiri Pirko pointed out in a review of ethtool netlink interface, rtnetlink is much more suitable for it so let's add it to the RTM_NEWLINK message. Add IFLA_PERM_ADDRESS attribute to RTM_NEWLINK messages unless the permanent address is all zeros (i.e. device driver did not fill it). As permanent address is not modifiable, reject userspace requests containing IFLA_PERM_ADDRESS attribute. Note: we already provide permanent hardware address for bond slaves; unfortunately we cannot drop that attribute for backward compatibility reasons. v5 -> v6: only add the attribute if permanent address is not zero

MKMichal Kubecek committed 6 years ago