> It's _BITUL() or so from linux/const.h.
> https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/const.h#L28
> You may not use internal definitions in UAPI headers.

Sorry, I missed it was an uapi header and gave the authors bad advice
with BIT.

If I get another fixed version by Saturday evening (CEST), I can still
squeeze it into my pull request for 5.14. Minor details can be fixed
incrementally, but we definatel need to get the uapi header correct.