security_task_prctl: why -ENOSYS

[William Roberts]

<snip>
>
> How about security_task_prctl_allowed()?  (Mirroring security_uring_*)
>
> Renaming the existing hook security_task_prctl_handle() also wouldn't
> be too bad, but that's probably more churn than it's worth.
>

Yeah if something else is already done, I'll just copy their
convention. I went with suffix _check for now.

Another possible issue that I think other upstream communities may
have with adding an additional hook, is that there will be two hooks
in the prctl syscall path,
I am not sure if that's a show stopper?