LU-3238 ptlrpc: expression expansion bug in macro

LU-3238 ptlrpc: expression expansion bug in macro

slab flag passed into __OBD_SLAB_ALLOC_VERBOSE is not bracketed,
so __OBD_SLAB_ALLOC_VERBOSE will get wrong value from unexpected
expression expansion and hit assertion.

Signed-off-by: Liang Zhen <liang.zhen@intel.com>
Change-Id: I4f09ccf743d6bda765bab64c60801a87d9a6b9b5
Reviewed-on: http://review.whamcloud.com/6190
Tested-by: Hudson
Reviewed-by: Nikitas Angelinas <nikitas_angelinas@xyratex.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>