LU-8130 libcfs: support latest rhashtable API

LU-8130 libcfs: support latest rhashtable API

With the broad support range of the OpenSFS lustre version pieces
are missing in some distributions to properly support using the
rhashtable API as required by Lustre.

Change-Id: I7ce2949ca2f1d497dcb60a8b17b964e47cdff223
Test-Parameters: trivial
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/34036
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>