WordPress: Add secondary navigation to end of primary navigation in PHP for mobile.

wp_secondary_primary_nav.php

<div class="main-navigation-container">
  <nav id="site-navigation" class="main-navigation navigation" role="navigation">
    <?php
    $secondary_nav = wp_nav_menu( array(
        'theme_location' => 'secondary',
        'echo' => false,
        'items_wrap' => '%3$s',
        'container' => false
    ) );

    //Add $secondary_nav to end so we can include it in our mobile navigation
    wp_nav_menu( array( 
        'theme_location'  => 'primary',
        'items_wrap'      => '<ul id="%1$s" class="%2$s">%3$s' . $secondary_nav . '</ul>',
    ) ); ?>
  </nav><!-- #site-navigation -->
</div>