LU-3281 obdclass: remove structure holes to reduce memory

LU-3281 obdclass: remove structure holes to reduce memory

Fix the alignment of fields in commonly-used structures to reduce
memory usage on the client and server.  Structures fixed:

ptlrpc_reply_state: reduced by 8 bytes
obd_device:         reduced by 16 bytes
niobuf_local:       reduced by 8 bytes

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: Ibe50c02e7ba823e337e846f90c6267cffc3ebbe5
Reviewed-on: http://review.whamcloud.com/16692
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>