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: I8b3398d534fbae683722f942403e031c68023b16
Signed-off-by: Lai Siyao <laisiyao@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/4277
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>