selftests: kmod: Add module address visibility test

Make sure we don't regress the CAP_SYSLOG behavior of the module address
visibility via /proc/modules nor /sys/module/*/sections/*.

Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>