rtnl_neightbl: decode ndtmsg netlink attributes

rtnl_neightbl: decode ndtmsg netlink attributes

* configure.ac (AC_CHECK_TYPES): Check for ndt_config
and ndt_stats structures in <linux/neighbour.h>.
(AC_CHECK_MEMBERS): Check for ndts_table_fulls field in struct ndt_stats.
* rtnl_neightbl.c: Include "xlat/rtnl_neightbl_parms_attrs.h".
(decode_ndt_config, decode_ndta_parms, decode_ndta_parms): New functions.
(ndt_parms_nla_decoders, ndtmsg_nla_decoders): New arrays.
(decode_ndtmsg): Use ndtmsg_nla_decoders.
* xlat/rtnl_neightbl_parms_attrs.in: New file.