Change network validation probe default configs

    private static final String TAG = NetworkMonitor.class.getSimpleName();

    private static final boolean DBG = false;

    // Default urls for captive portal detection probes

    private static final String DEFAULT_HTTPS_URL     =

            "https://connectivitycheck.gstatic.com/generate_204";

    // Default configuration values for captive portal detection probes.

    // TODO: append a random length parameter to the default HTTPS url.

    // TODO: randomize browser version ids in the default User-Agent String.

    private static final String DEFAULT_HTTPS_URL     = "https://www.google.com/generate_204";

    private static final String DEFAULT_HTTP_URL      =

            "http://connectivitycheck.gstatic.com/generate_204";

    private static final String DEFAULT_FALLBACK_URL  = null;

    private static final String DEFAULT_USER_AGENT    = null;

    private static final String DEFAULT_FALLBACK_URL  = "http://www.google.com/gen_204";

    private static final String DEFAULT_USER_AGENT    = "Mozilla/5.0 (X11; Linux x86_64) "

                                                      + "AppleWebKit/537.36 (KHTML, like Gecko) "

                                                      + "Chrome/52.0.2743.82 Safari/537.36";

    private static final int SOCKET_TIMEOUT_MS = 10000;

    private static final int PROBE_TIMEOUT_MS  = 3000;