tests: kernel: userspace: extend bad syscall-ID test-case

Extend the bad syscall-ID test case to cover
erroneously supplied larged unsiged syscall-ID
values.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
Signed-off-by: David Brown <david.brown@linaro.org>