Comment # 27 on bug 1191795 from Oliver Neukum

Working hypothesis:

static int rtl8169_runtime_suspend(struct device *device)
{
        struct rtl8169_private *tp = dev_get_drvdata(device);

        if (!tp->TxDescArray) {
                netif_device_detach(tp->dev);
                return 0;
        }

This test is wrong. I'll make a test kernel that omits it.