sysctl: call sysctl tests with a for loop
As we add more test functions in lib/tests_sysctl the main test function
(test_sysctl_init) grows. Condense the logic to make it easier to
add/remove tests.
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Joel Granados <joel.granados@kernel.org>