Re: [PATCH 2/2] UBI: support per-device wear-leveling threshold

[Ran Hongyun]

Reply to the issues raised by sashiko: The struct size is unchanged,
and all existing userspace programs zero-initialize the struct
ubi_attach_req, so wl_threshold reads as zero and falls back to 
CONFIG_MTD_UBI_WL_THRESHOLD. No backward compatibility issue.