LU-11518 ldlm: cancel LRU improvement

LU-11518 ldlm: cancel LRU improvement

Add @batch parameter to cancel LRU, which means if at least 1 lock is
cancelled, try to cancel at least a batch locks. This functionality
will be used in later patches.

Limit the LRU cancel by 1 thread only, however, not for those which
have the @max limit given (ELC), as LRU may be left not cleaned up
in full.

Signed-off-by: Vitaly Fertman <c17818@cray.com>
Change-Id: Ide21c4a2b2209b8a721249466ea1e651c8532c8a
HPE-bug-id: LUS-8678
Reviewed-on: https://es-gerrit.dev.cray.com/157067
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Tested-by: Alexander Lezhoev <c17454@cray.com>
Reviewed-on: https://review.whamcloud.com/39561
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Gu Zheng <gzheng@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>