Store write hint from original bio in stripe head so it can be assigned
to bio sent to each RAID device.
Signed-off-by: NMariusz Dabrowski <mariusz.dabrowski@intel.com>
Reviewed-by: NArtur Paszkiewicz <artur.paszkiewicz@intel.com>
Reviewed-by: NPawel Baldysiak <pawel.baldysiak@intel.com>
Signed-off-by: NShaohua Li <shli@fb.com>