LU-20 kernel: increase BH_LRU_SIZE to 16

LU-20 kernel: increase BH_LRU_SIZE to 16

As kernel community did not want a complicated way of
modifying BH_LRU_SIZE, it was proposed to directly set it
to 16. This has been accepted.
This patch is merged in the upstream kernel:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/
linux.git/commit/?id=86cf78d73de8c6bfa89804b91ee0ace71a459961

Signed-off-by: Sebastien Buisson <sebastien.buisson@bull.net>
Change-Id: I71fb455de9ec70ed90f86d402ae76ecfba1e1e61
Reviewed-on: http://review.whamcloud.com/12577
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>