LU-7828 statahead: set sai_index_wait with lli_sa_lock held

LU-7828 statahead: set sai_index_wait with lli_sa_lock held

It is the sponsor thread of the statahead thread to update the
sai::sai_index_wait. Originally, it didn't hold the lli_sa_lock
when did that. Becuase of out-of-order execution others may miss
to wakeup such thread.

On the other hand, if the statahead RPC gets failure, it should
wakeup the sponsor thread, not the statahead thread.

Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Icc7937794ff62c2aa6f7d456defffdfc5ba53b61
Reviewed-on: http://review.whamcloud.com/18499
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>