LU-4008 mdt: Use actual size for layout lock intents

LU-4008 mdt: Use actual size for layout lock intents

The intent for layout looks up the size of the lov xattr. That size
should be used for the reply buffer instead of the maximum size ever
seen.

Signed-off-by: Matt Ezell <ezellma@ornl.gov>
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I9550aa47313502288b018f5cac0d59931ce76d21
Reviewed-on: http://review.whamcloud.com/9571
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>