Some operations like interface creation may need to return metadata - in this case, interface name - back to the caller if the operation is successful.
This change implements attaching an NLMSGERR_ATTR_COOKIE nla to the operation reply message via nlmsg_report_cookie().
Additionally, on successful interface creation, interface index and interface name are returned in the IFLA_NEW_IFINDEX and IFLA_IFNAME TLVs, encapsulated in the NLMSGERR_ATTR_COOKIE`.
MFC after: 1 week