xfs: report the correct read/write dio alignment for reflinked inodes

xfs: report the correct read/write dio alignment for reflinked inodes

For I/O to reflinked blocks we always need to write an entire new
file system block, and the code enforces the file system block alignment
for the entire file if it has any reflinked blocks.

Use the new STATX_DIO_READ_ALIGN flag to report the asymmetric read
vs write alignments for reflinked files.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250109083109.1441561-5-hch@lst.de
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>