LU-7581 ldiskfs: RHEL7.2 fix wrong EA inode backpointer check

LU-7581 ldiskfs: RHEL7.2 fix wrong EA inode backpointer check

Port http://review.whamcloud.com/17675 for RHEL7.2:

	EA inode is linked back to the parent inode using
	i_mtime.tv_sec filed. An inode number bigger 2G gets
	mangled due to sign bit extension over the high bits
	of tv_sec. It causes parent backpointer checks to fail.
	Add an explicit integer type conversion to ignore high
	bits of i_mtime.tv_sec.

	Alexander Zarochentsev <alexander.zarochentsev@seagate.com>

Fix other code style issues and comments for upstream kernel.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I7d402f000cde5ffb1ededf7a80276538e4465757
Reviewed-on: http://review.whamcloud.com/18436
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>