LU-16272 libcfs: cfs_hash_for_each_empty optimization

LU-16272 libcfs: cfs_hash_for_each_empty optimization

Restarts from bucket 0 in cfs_hash_for_each_empty()
cause excessive cpu consumption while checking first empty
buckets.

Lustre-change: https://review.whamcloud.com/48972
Lustre-commit: 306a9b666e5ea2882f704d93483355e7e147544f

HPE-bug-id: LUS-11311
Signed-off-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Change-Id: Ic03875ea25101052468213043128912ac46daf32
Reviewed-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53379
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>