xfs: actually rebuild the parent pointer xattrs

xfs: actually rebuild the parent pointer xattrs

Source kernel commit: a26dc21309af68623b82b4e366cbbeb5a85ce65b

Once we've assembled all the parent pointers for a file, we need to
are embedded in the xattr structure, which means that we must write a
new extended attribute structure, again, atomically.  Therefore, we must
copy the non-parent-pointer attributes from the file being repaired into
the temporary file's extended attributes and then call the atomic extent
swap mechanism to exchange the blocks.

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