vhost_net: use offload API instead of bypassing it

There is no need to access backend->info->has_vnet_hdr() and friends
anymore.  Use the qemu_has_vnet_hdr() API instead.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

hw/net/vhost_net.c

@@ -106,7 +106,7 @@ struct vhost_net *vhost_net_init(NetClientState *backend, int devfd,
         goto fail;
     }
     net->nc = backend;
-    net->dev.backend_features = backend->info->has_vnet_hdr(backend) ? 0 :
+    net->dev.backend_features = qemu_has_vnet_hdr(backend) ? 0 :
         (1 << VHOST_NET_F_VIRTIO_NET_HDR);
     net->backend = r;
 
@@ -117,7 +117,7 @@ struct vhost_net *vhost_net_init(NetClientState *backend, int devfd,
     if (r < 0) {
         goto fail;
     }
-    if (!backend->info->has_vnet_hdr_len(backend,
+    if (!qemu_has_vnet_hdr_len(backend,
                                sizeof(struct virtio_net_hdr_mrg_rxbuf))) {
         net->dev.features &= ~(1 << VIRTIO_NET_F_MRG_RXBUF);
     }