function atg_menu_classes($classes, $item, $args) {

  if($args->theme_location == 'secondary') {

    $classes[] = 'list-inline-item';

  }

  return $classes;

}

add_filter('nav_menu_css_class', 'atg_menu_classes', 1, 3);

add_filter( 'nav_menu_link_attributes', 'add_class_to_items_link', 10, 3 );

​

function add_class_to_items_link( $atts, $item, $args ) {

  // check if the item has children

  $hasChildren = (in_array('menu-item-has-children', $item->classes));

  if ($hasChildren) {

    // add the desired attributes:

    $atts['class'] = 'dropdown-toggle';

    $atts['data-toggle'] = 'dropdown';

    $atts['data-target'] = '#';

  }

  return $atts;

}