LU-2272 statahead: ll_intent_drop_lock() called in spinlock

LU-2272 statahead: ll_intent_drop_lock() called in spinlock

ll_intent_drop_lock() may sleep, which should not be called inside
spinlock.

This is back-ported from the following patch:
Lustre-change: http://review.whamcloud.com/9665

Test-Parameters: alwaysuploadlogs envdefinitions=SLOW=yes \
mdtcount=1 testlist=lustre-rsync-test,lustre-rsync-test

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Change-Id: Id658c0bd3b9dc0a918995c66842b0c3fabe8a7ae
Signed-off-by: Jian Yu <jian.yu@intel.com>
Reviewed-on: http://review.whamcloud.com/10674
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>