LU-1887 ptlrpc: grant shrink rpc format is special

LU-1887 ptlrpc: grant shrink rpc format is special

Grant shrink rpc is packed in OST_SET_INFO request, but its format is
different from others.

Change-Id: I24fef30504847d26699df427f787d7c1d594c7c5
Signed-off-by: Lai Siyao <laisiyao@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/4269
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>