xfs_repair: fix rmapbt record order check

xfs_repair: fix rmapbt record order check

The rmapbt record order checks here don't quite work properly.  For
non-shared filesystems, we fail to check that the startblock of the nth
record comes entirely after the previous record.

However, for filesystems with shared blocks (reflink) we correctly check
that the startblock/owner/offset of the nth record comes after the
previous one.

Therefore, make the reflink fs checks use "laststartblock" to preserve
that functionality while making the non-reflink fs checks use
"lastblock" to fix the problem outlined above.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>