selftests/seccomp: Pin benchmark to single CPU

The seccomp benchmark test (for validating the benefit of bitmaps) can
be sensitive to scheduling speed, so pin the process to a single CPU,
which appears to significantly improve reliability, and loosen the
"close enough" checking to allow up to 10% variance instead of 1%.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202402061002.3a8722fd-oliver.sang@intel.com


Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>