LU-9230 ldlm: speed up preparation for list of lock cancel

LU-9230 ldlm: speed up preparation for list of lock cancel

Keep the skipped locks in lru list will cause serious
contention for ns_lock. Since we have to travel them
every time in the ldlm_prepare_lru_list(). So we will
use a cursor to record position that last accessed
lock in lru list.

Change-Id: Ibda36a90e54076cb785a65910b34300639b3e140
Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Signed-off-by: Sergey Cheremencev <c17829@cray.com>
Reviewed-on: https://review.whamcloud.com/26327
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Jenkins
Reviewed-by: Vitaly Fertman <c17818@cray.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>