LU-3027 lov: to not modify lov lock when sublock is canceled

LU-3027 lov: to not modify lov lock when sublock is canceled

Otherwise it will cause wrong lock to be enqueued.

lls_ever_canceled is introduced to solve potential performance
problem by this patch.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I1ea62902c9d1a468f5952f30a8dc5dec22b8bb1c
Reviewed-on: http://review.whamcloud.com/7841
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>