LU-4579 ldlm: Properly display time on lock timeout

When lock timeout happens, need to printtime since last lock
activity, not since when the lock was granted.
As such set l_last_activity to current time when sending callbacks too.

Change-Id: I31d0de6d9add67865cfcb16af903647f7cb932a0
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Reviewed-on: http://review.whamcloud.com/10601
Tested-by: Jenkins
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>