From Linux 6.6, `uffdio_register.iotcls` contains a bit for `_UFFDIO_POISON` ([code](https://elixir.bootlin.com/linux/v6.6/source/include/uapi/linux/userfaultfd.h#L54)). register() always fails as `UnrecognizedIoctls(284)` because `struct IoctlFlags` does not support `UFFDIO_POISON` yet.
