LU-3205 llite: Set layout_gen before compatibility check

LU-3205 llite: Set layout_gen before compatibility check

We should set IO's layout generation to current generation of inode,
no matter what it is. Otherwise, it will go into an infinite loop
on layout change check.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I9f1f0d9ae0dd53dea130db46bbcbdbd29526b6eb
Reviewed-on: http://review.whamcloud.com/6137
Tested-by: Hudson
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>