ocfs2: Add ecc and checksums to ocfs2 xattr buckets.

The xattr bucket can span multiple blocks on disk.  We have wrappers
for this structure in the code.  We use the new multi-block ecc calls to
calculate and validate the bucket.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>