generic: test XFS forkoff miscalcution on 32-bit platform

generic: test XFS forkoff miscalcution on 32-bit platform

There is a regression that recent XFS_LITINO(mp) update causes
xfs_attr_shortform_bytesfit() returns maxforkoff rather than 0.

Therefore, one result is
  "ASSERT(new_size <= XFS_IFORK_SIZE(ip, whichfork));"

Add a regression test in fstests generic to look after that since
the testcase itself isn't xfs-specific.

Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>