xfs: verify inode buffers as they are read from disk

Add an inode buffer verify callback function and pass it into the
buffer read functions. Inodes are special in that the verbose checks
will be done when reading the inode, but we still need to sanity
check the buffer when that is first read. Always verify the magic
numbers in all inodes in the buffer, rather than jus ton debug
kernels.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Phil White <pwhite@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>