henrijs

function themename_menu_link(&$variables) {
  $element = $variables['element'];
  $sub_menu = '';

  $element['#attributes']['data-menu-parent'] = $element['#original_link']['menu_name'] . '-' . $element['#original_link']['depth'];

  if ($element['#below']) {
    $sub_menu = drupal_render($element['#below']);
  }