LU-4193 ldiskfs: increase max journal to 4GB

LU-4193 ldiskfs: increase max journal to 4GB

Increase the maximum journal size to 4GB to handle the increased
metadata operation rate possible since MDT SMP scaling is done.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I025b68f9f8b7c9d1084f704e2ebf8722753ebbe5
Reviewed-on: http://review.whamcloud.com/8111
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>