repair: detect and handle attribute tree CRC errors

repair: detect and handle attribute tree CRC errors

Currently the attribute code will not detect and correct errors in
the attribute tree. It also fails to validate the CRCs and headers
on remote attribute blocks. Ensure that all the attribute blocks are
CRC checked and that the processing functions understand the correct
block formats for decoding.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>