virtio: correctly initialize vm_running

Current vm_running was not explicitly initialized and its value was changed by
vm state notifier, this may confuse the virtio device being hotplugged such as
virtio-net with vhost backend as it may think the vm was not running. Solve this
by initialize this value explicitly in virtio_common_init().
Signed-off-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio.c

@@ -787,6 +787,7 @@ VirtIODevice *virtio_common_init(const char *name, uint16_t device_id,
     vdev->queue_sel = 0;
     vdev->config_vector = VIRTIO_NO_VECTOR;
     vdev->vq = qemu_mallocz(sizeof(VirtQueue) * VIRTIO_PCI_QUEUE_MAX);
+    vdev->vm_running = vm_running;
     for(i = 0; i < VIRTIO_PCI_QUEUE_MAX; i++) {
         vdev->vq[i].vector = VIRTIO_NO_VECTOR;
         vdev->vq[i].vdev = vdev;