get_option in header.php not returning value from customizer

There are two ways to solve this:

1 Keep the mods as they are and use get_theme_mod in stead of get_option

2 Store the mods as options by changing the setting:

$wp_customize->add_setting( 'social_link_facebook' , array(
    'default' => '',
    'type' => 'option'
) );