rtnl_link: add decoding of new IFLA_* attributes

rtnl_link: add decoding of new IFLA_* attributes

* xlat/rtnl_link_attrs.in (IFLA_NEW_NETNSID, IFLA_IF_NETNSID,
IFLA_CARRIER_UP_COUNT, IFLA_CARRIER_DOWN_COUNT, IFLA_NEW_IFINDEX): New
constants introduced by linux kernel commits v4.15-rc1~84^2~557,
v4.15-rc1~84^2~133^2, v4.16-rc1~123^2~91, and v4.16-rc1~123^2~24^2.
* rtnl_link.c (ifinfomsg_nla_decoders) <IFLA_NEW_NETNSID,
IFLA_IF_NETNSID, IFLA_CARRIER_UP_COUNT, IFLA_CARRIER_DOWN_COUNT,
IFLA_NEW_IFINDEX>: New items.