libnl-tiny: backport 'gnet_stats_rate_est64' support

This has been added to the kernel uapi for a while, and makes
sense to have it here too.
At the moment we're using it for query-ing qdisc via netlink
using libnl-tiny.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

SVN-Revision: 49188