libext2fs: zero hash in ibody extended attributes

libext2fs: zero hash in ibody extended attributes

The kernel never updates the extended attribute hash value for
attributes stored in the inode.  However, fsck has always checked this
value (if it's nonzero) and will complain if the hash doesn't match
the xattr.  Therefore, always zero the hash value when writing to
in-ibody xattrs to avoid creating "corrupt" attribute errors
downstream.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>