vhost-vdpa: don't initialize backend_features

We used to initialize backend_features during vhost_vdpa_init()
regardless whether or not it was supported by vhost. This will lead
the unsupported features like VIRTIO_F_IN_ORDER to be included and set
to the vhost-vdpa during vhost_dev_start. Because the
VIRTIO_F_IN_ORDER is not supported by vhost-vdpa so it won't be
advertised to guest which will break the datapath.

Fix this by not initializing the backend_features, so the
acked_features could be built only from guest features via
vhost_net_ack_features().

Fixes: 108a648 ("vhost-vdpa: introduce vhost-vdpa backend")
Cc: qemu-stable@nongnu.org
Cc: Gautam Dawar <gdawar@xilinx.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/virtio/vhost-vdpa.c

@@ -268,15 +268,12 @@ static void vhost_vdpa_add_status(struct vhost_dev *dev, uint8_t status)
 static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque)
 {
     struct vhost_vdpa *v;
-    uint64_t features;
     assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_VDPA);
     trace_vhost_vdpa_init(dev, opaque);
 
     v = opaque;
     v->dev = dev;
     dev->opaque =  opaque ;
-    vhost_vdpa_call(dev, VHOST_GET_FEATURES, &features);
-    dev->backend_features = features;
     v->listener = vhost_vdpa_memory_listener;
     v->msg_type = VHOST_IOTLB_MSG_V2;