socketutils: build a dynamic xlat table for NETLINK_GENERIC decoding

socketutils: build a dynamic xlat table for NETLINK_GENERIC decoding

* configure.ac (AC_CHECK_HEADERS): Add linux/genetlink.h.
* defs.h (genl_families_xlat): New prototype.
* socketutils.c [HAVE_LINUX_GENETLINK_H]: Include <linux/genetlink.h>.
[HAVE_LINUX_GENETLINK_H] (genl_send_dump_families,
genl_parse_families_response): New helper functions.
(genl_families_xlat): New function for building the xlat table
for NETLINK_GENERIC decoding.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>