xfs: repair directory parent pointers by scanning for dirents

xfs: repair directory parent pointers by scanning for dirents

If parent pointers are enabled on the filesystem, we can repair the
entire dataset by walking the directories of the filesystem looking for
dirents that we can turn into parent pointers.  Once we have a full
incore dataset, we'll figure out what to do with it, but that's for a
subsequent patch.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>