integrate wp-pagenavi twenty eleven

this is the original code from Twenty Eleven functions.php

**
 * Display navigation to next/previous pages when applicable
 */
function twentyeleven_content_nav( $nav_id ) {
    global $wp_query;

    if ( $wp_query->max_num_pages > 1 ) : ?>
        <nav id="<?php echo $nav_id; ?>">
            <h3 class="assistive-text"><?php _e( 'Post navigation', 'twentyeleven' ); ?></h3>
            <div class="nav-previous"><?php next_posts_link( __( '<span class="meta-nav">&larr;</span> Older posts', 'twentyeleven' ) ); ?></div>
            <div class="nav-next"><?php previous_posts_link( __( 'Newer posts <span class="meta-nav">&rarr;</span>', 'twentyeleven' ) ); ?></div>
        </nav><!-- #nav-above -->
    <?php endif;
}

this is edited to work with wp-pagenavi plugin

/**
 * Display navigation to next/previous pages when applicable
 */
function twentyeleven_content_nav( $nav_id ) {
    global $wp_query;

    if ( $wp_query->max_num_pages > 1 ) : ?>
        <nav id="<?php echo $nav_id; ?>">
            <h3 class="assistive-text"><?php _e( 'Post navigation', 'twentyeleven' ); ?></h3>
<?php if( function_exists('wp_pagenavi') ) : ?>
            <div class="pagenavi"><?php wp_pagenavi(); ?></div>

<?php else : ?>
            <div class="nav-previous"><?php next_posts_link( __( '<span class="meta-nav">&larr;</span> Older posts', 'twentyeleven' ) ); ?></div>
            <div class="nav-next"><?php previous_posts_link( __( 'Newer posts <span class="meta-nav">&rarr;</span>', 'twentyeleven' ) ); ?></div>

<?php endif; ?>
        </nav><!-- #nav-above -->
    <?php endif;
}