rtnl_link: decode more ifinfomsg netlink attributes

rtnl_link: decode more ifinfomsg netlink attributes

* configure.ac (AC_CHECK_TYPES): Check for struct ifla_port_vsi
in <linux/if_link.h>.
* rtnl_link.c: Include "xlat/rtnl_ifla_info_attrs.h",
"xlat/rtnl_ifla_port_attrs.h", "xlat/rtnl_ifla_port_attrs.h",
"xlat/rtnl_ifla_xdp_attrs.h", and "xlat/xdp_flags.h".
(decode_ifla_linkinfo, decode_ifla_port_vsi,
decode_ifla_port, decode_ifla_vf_ports,
decode_ifla_xdp_flags, decode_ifla_xdp): New functions.
(ifla_linkinfo_nla_decoders, ifla_port_nla_decoders,
ifla_vf_port_nla_decoders, ifla_xdp_nla_decoders): New arrays.
(ifinfomsg_nla_decoders) <IFLA_LINKINFO>: Use decode_ifla_linkinfo.
<IFLA_VF_PORTS>: Use decode_ifla_vf_ports.
<IFLA_PORT_SELF>: Use decode_ifla_port.
<IFLA_XDP>: Use decode_ifla_xdp.
* xlat/rtnl_ifla_info_attrs.in: New file.
* xlat/rtnl_ifla_port_attrs.in: Likewise.
* xlat/rtnl_ifla_vf_port_attrs.in: Likewise.
* xlat/rtnl_ifla_xdp_attrs.in: Likewise.
* xlat/xdp_flags.in: Likewise.