Custom Hook - generate_bottom_of_primary_menu.php

//Custom Hook is: generate_bottom_of_primary_menu

add_shortcode('bottom_of_primary_menu_hook', function($atts){
	ob_start();
        $atts = shortcode_atts( array(
            'hook_name' => 'bottom of menu'
        ), $atts, 'bottom_of_primary_menu_hook' );
		do_action($atts['hook_name']);
	return ob_get_clean();
});

add_filter( 'wp_nav_menu_items', 'prefix_add_div', 15, 2 );
function prefix_add_div( $items, $args ) {
	if( $args->theme_location != 'primary' ) {
        return $items;
    }
    $items .= '<li class="menu-item custom-menu-item">'.do_shortcode( '[bottom_of_primary_menu_hook hook_name="generate_bottom_of_primary_menu"]' ).'</li>'. $items;
    return $items;
}