@media only screen and (max-width: 600px) {
    .container-fluid {
        padding:0; /* Extend your menu really full width without padding of container-fluid */
    }
    .navbar-nav {
        margin:0; /* Center your menu with current 100% width available */
    }
    .navbar .nav > li {
        display: block;
    }
    .navbar .nav > li  img {
        margin: auto;
    }
}