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.

Lustre-change: https://review.whamcloud.com/34036
Lustre-commit: 8de7221201c0707245c9ee2ef7cdd1d54207b3ee

Change-Id: I7ce2949ca2f1d497dcb60a8b17b964e47cdff223
Test-Parameters: trivial
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/35143
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>