Ignore loss of IPv6 provisioning when not avoiding bad Wi-Fi. am: f11ee9f5

    // object that is a correct and complete assessment of what changed, taking

    // account of the asymmetries described in the comments in this function.

    // Then switch to using it everywhere (IpReachabilityMonitor, etc.).

    private static ProvisioningChange compareProvisioning(

    private ProvisioningChange compareProvisioning(

            LinkProperties oldLp, LinkProperties newLp) {

        ProvisioningChange delta;

        final boolean lostIPv4Address = oldLp.hasIPv4Address() && !newLp.hasIPv4Address();

        final boolean lostIPv6Router = oldLp.hasIPv6DefaultRoute() && !newLp.hasIPv6DefaultRoute();

        // If bad wifi avoidance is disabled, then ignore IPv6 loss of

        // provisioning. Otherwise, when a hotspot that loses Internet

        // access sends out a 0-lifetime RA to its clients, the clients

        // will disconnect and then reconnect, avoiding the bad hotspot,

        // instead of getting stuck on the bad hotspot. http://b/31827713 .

        //

        // This is incorrect because if the hotspot then regains Internet

        // access with a different prefix, TCP connections on the

        // deprecated addresses will remain stuck.

        //

        // Note that we can still be disconnected by IpReachabilityMonitor

        // if the IPv6 default gateway (but not the IPv6 DNS servers; see

        // accompanying code in IpReachabilityMonitor) is unreachable.

        final boolean ignoreIPv6ProvisioningLoss = !mAvoidBadWifiTracker.currentValue();

        // Additionally:

        //

        // Partial configurations (e.g., only an IPv4 address with no DNS

        // Because on such a network isProvisioned() will always return false,

        // delta will never be LOST_PROVISIONING. So check for loss of

        // provisioning here too.

        if (lostIPv4Address || lostIPv6) {

        if (lostIPv4Address || (lostIPv6 && !ignoreIPv6ProvisioningLoss)) {

            delta = ProvisioningChange.LOST_PROVISIONING;

        }

        // If the previous link properties had a global IPv6 address and an

        // IPv6 default route then also consider the loss of that default route

        // to be a loss of provisioning. See b/27962810.

        if (oldLp.hasGlobalIPv6Address() && lostIPv6Router) {

        if (oldLp.hasGlobalIPv6Address() && (lostIPv6Router && !ignoreIPv6ProvisioningLoss)) {

            delta = ProvisioningChange.LOST_PROVISIONING;

        }