[Bug 200802] MAXCPU bump to 256 breaks ABI for cpuset_getaffinity/setaffinity

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=200802

--- Comment #7 from Ed Maste <emaste@freebsd.org> ---
(In reply to Dmitry Chagin from comment #6)

I guess the main change related to this is:

commit f35093f8d6d8155ab2e56c11ee03d474688b16a2
Author: Dmitry Chagin <dchagin@FreeBSD.org>
Date:   Wed May 11 10:36:01 2022 +0300

    Use Linux semantics for the thread affinity syscalls.

    Linux has more tolerant checks of the user supplied cpuset_t's.

    Minimum cpuset_t size that the Linux kernel permits in case of
    getaffinity() is the maximum CPU id, present in the system / NBBY,
    the maximum size is not limited.
    For setaffinity(), Linux does not limit the size of the user-provided
    cpuset_t, internally using only the meaningful part of the set, where
    the upper bound is the maximum CPU id, present in the system, no larger
    than the size of the kernel cpuset_t.
    Unlike FreeBSD, Linux ignores high bits if set in the setaffinity(),
    so clear it in the sched_setaffinity() and Linuxulator itself.

    Reviewed by:            Pau Amma (man pages)
    In collaboration with:  jhb
    Differential revision:  https://reviews.freebsd.org/D34849
    MFC after:              2 weeks

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