LU-7261 ldiskfs: fix large_xattr overwrite

LU-7261 ldiskfs: fix large_xattr overwrite

Handle the case where a large (external inode) xattr is being replaced
correctly.  The special case for this in ext4_set_xattr() was
incorrectly setting the offset of the xattr data within the inode
when it shouldn't have.

Add an e2fsck check of the large_xattr filesystem in conf-sanity
test_61 to verify this is working correctly.

Signed-off-by: Alexey Lyashkov <alexey.lyashkov@seagate.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I27123d7985eff0538b6f64139cebc2f0f1806260
Reviewed-on: http://review.whamcloud.com/16777
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>