xfs: apply rt extent alignment constraints to CoW extsize hint

xfs: apply rt extent alignment constraints to CoW extsize hint

The copy-on-write extent size hint is subject to the same alignment
constraints as the regular extent size hint.  Since we're in the process
of adding reflink (and therefore CoW) to the realtime device, we must
apply the same scattered rextsize alignment validation strategies to
both hints to deal with the possibility of rextsize changing.

Therefore, fix the inode validator to perform rextsize alignment checks
on regular realtime files, and to remove misaligned directory hints.

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