Form submission handler for statistics_settings_form().
function statistics_settings_form_submit($form, &$form_state) {
config('statistics.settings')
->set('access_log.enabled', $form_state['values']['statistics_enable_access_log'])
->set('access_log.max_lifetime', $form_state['values']['statistics_flush_accesslog_timer'])
->set('count_content_views', $form_state['values']['statistics_count_content_views'])
->save();
}