xfs_repair: validate CoW extent size hint on rtinherit directories

xfs_repair: validate CoW extent size hint on rtinherit directories

XFS allows a sysadmin to change the rt extent size when adding a rt
section to a filesystem after formatting.  If there are any directories
with both a cowextsize hint and rtinherit set, the hint could become
misaligned with the new rextsize.  Offer to fix the problem if we're in
modify mode and the verifier didn't trip.  If we're in dry run mode,
we let the kernel fix it.

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