code from blog post: http://scrawlon.com/2015/09/21/add-more-social-media-options-to-wordpress-divi-theme/

custom_options_divi.php

<?php

require_once( get_template_directory() . esc_attr( "/options_divi.php" ) );
global $options;
$epanel_key = "name";
$epanel_value = "Show RSS Icon";

$custom_options = array (
	array( "name" => esc_html__( "Show GitHub Icon", $themename ),
           "id" => $shortname."_show_github_icon",
           "type" => "checkbox",
           "std" => "on",
           "desc" => esc_html__( "Here you can choose to display the GitHub Icon. ", $themename ) ),

	array( "name" => esc_html__( "Show LinkedIn Icon", $themename ),
           "id" => $shortname."_show_linkedin_icon",
           "type" => "checkbox2",
           "std" => "on",
           "desc" => esc_html__( "Here you can choose to display the LinkedIn Icon on your homepage. ", $themename ) ),

	array( "name" => esc_html__( "GitHub Profile Url", $themename ),
           "id" => $shortname."_github_url",
           "std" => "#",
           "type" => "text",
           "validation_type" => "url",
		   "desc" => esc_html__( "Enter the URL of your GitHub feed. ", $themename ) ),

	array( "name" => esc_html__( "LinkedIn Profile Url", $themename ),
           "id" => $shortname."_linkedin_url",
           "std" => "#",
           "type" => "text",
           "validation_type" => "url",
		   "desc" => esc_html__( "Enter the URL of your LinkedIn Profile. ", $themename ) )

);

foreach( $options as $index => $value ) {
    if ( isset($value[$epanel_key]) && $value[$epanel_key] === $epanel_value ) {
        foreach( $custom_options as $custom_index => $custom_option ) {
            $options = insertArrayIndex($options, $custom_option, $index+$custom_index+1);
        }
        break;
    }
}


function insertArrayIndex($array, $new_element, $index) {
	$start = array_slice($array, 0, $index);
	$end = array_slice($array, $index);
	$start[] = $new_element;

	return array_merge($start, $end);
}

return $options;

functions.php

function load_custom_core_options() {
    if ( ! function_exists( 'et_load_core_options' ) ) {
        function et_load_core_options() {
            $options = require_once( get_stylesheet_directory() . esc_attr( "/epanel/custom_options_divi.php" ) );
        }
    }
}
add_action( 'after_setup_theme', 'load_custom_core_options' )

social_icons.php

<ul class="et-social-icons">

    <?php
        $social_sites = array(
            "facebook"  => "fa-facebook",
            "twitter"   => "fa-twitter",
            "github"    => "fa-github",
            "linkedin"  => "fa-linkedin",
            "google"    => "fa-google-plus"
        );
    ?>

    <?php foreach( $social_sites as $social_site => $social_icon ): ?>
        <?php if ( 'on' === et_get_option( 'divi_show_' . $social_site . '_icon', 'on' ) ) : ?>
            <li class="et-social-icon">
                <a href="<?php echo esc_url( et_get_option( 'divi_' . $social_site . '_url', '#' ) ); ?>" target="_blank" class="icon">
                    <i class="fa <?php echo $social_icon; ?>"></i>
                </a>
            </li>
        <?php endif; ?>
    <?php endforeach; ?>

    <?php if ( 'on' === et_get_option( 'divi_show_rss_icon', 'on' ) ) : ?>
    <?php
        $et_rss_url = '' !== et_get_option( 'divi_rss_url' )
            ? et_get_option( 'divi_rss_url' )
            : get_bloginfo( 'rss2_url' );
    ?>
        <li class="et-social-icon">
            <a href="<?php echo esc_url( $et_rss_url ); ?>" target="_blank" class="icon">
                <i class="fa fa-rss"></i>
            </a>
        </li>
    <?php endif; ?>

</ul>