virtio-net: don't allocate control_buf if not supported

Not all virtio_net devices support the ctrl queue feature. Thus, there
is no need to allocate unused resources.
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Link: https://lore.kernel.org/r/20210502093319.61313-1-mgurtovoy@nvidia.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/net/virtio_net.c

@@ -2801,9 +2801,13 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
 {
 	int i;
 
+	if (vi->has_cvq) {
 		vi->ctrl = kzalloc(sizeof(*vi->ctrl), GFP_KERNEL);
 		if (!vi->ctrl)
 			goto err_ctrl;
+	} else {
+		vi->ctrl = NULL;
+	}
 	vi->sq = kcalloc(vi->max_queue_pairs, sizeof(*vi->sq), GFP_KERNEL);
 	if (!vi->sq)
 		goto err_sq;