Previously 'btrfs check --check-data-csum' will report tons of false
alerts for RAID56.
Add a test case to make sure with the new RAID56 rebuild ability, there
should be no false alerts.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
