virtio-pci: unbreak queue_enable read

Guest always get zero when reading queue_enable. This violates
spec. Fixing this by setting the queue_enable to true during any guest
writing and setting it to zero during reset.

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-pci.c

@@ -1384,6 +1384,7 @@ static void virtio_pci_common_write(void *opaque, hwaddr addr,
                        proxy->vqs[vdev->queue_sel].avail[0],
                        ((uint64_t)proxy->vqs[vdev->queue_sel].used[1]) << 32 |
                        proxy->vqs[vdev->queue_sel].used[0]);
+        proxy->vqs[vdev->queue_sel].enabled = 1;
         break;
     case VIRTIO_PCI_COMMON_Q_DESCLO:
         proxy->vqs[vdev->queue_sel].desc[0] = val;
@@ -1831,9 +1832,15 @@ static void virtio_pci_reset(DeviceState *qdev)
 {
     VirtIOPCIProxy *proxy = VIRTIO_PCI(qdev);
     VirtioBusState *bus = VIRTIO_BUS(&proxy->bus);
+    int i;
+
     virtio_pci_stop_ioeventfd(proxy);
     virtio_bus_reset(bus);
     msix_unuse_all_vectors(&proxy->pci_dev);
+
+    for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
+        proxy->vqs[i].enabled = 0;
+    }
 }
 
 static Property virtio_pci_properties[] = {