LU-8130 libcfs: port working hash from upstream

LU-8130 libcfs: port working hash from upstream

The hash_[32|64] function in pre-4.6 kernels produce hashes
with poor distributions which result in high collision rates.
Backport those improvements for the pre-4.6 kernels Lustre
supports. Details can be read here:

https://lwn.net/Articles/687494

Test-Parameters: trivial
Change-Id: Id2436ba8be2d3ed482c5386b79710f594d5b3e59
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/33789
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>