Revert "vhost: send SET_VRING_ENABLE at start/stop"

This reverts commit 3a12f322.

In case of live migration several queues can be enabled and not only the
first one. So informing backend that only the first queue is enabled is
wrong.
Reported-by: NThibaut Collet <thibaut.collet@6wind.com>
Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NYuanhan Liu <yuanhan.liu@linux.intel.com>

hw/virtio/vhost.c

@@ -1226,11 +1226,6 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
         }
     }
 
-    if (hdev->vhost_ops->vhost_set_vring_enable) {
-        /* only enable first vq pair by default */
-        hdev->vhost_ops->vhost_set_vring_enable(hdev, hdev->vq_index == 0);
-    }
-
     return 0;
 fail_log:
     vhost_log_put(hdev, false);
@@ -1261,10 +1256,6 @@ void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev)
                              hdev->vq_index + i);
     }
 
-    if (hdev->vhost_ops->vhost_set_vring_enable) {
-        hdev->vhost_ops->vhost_set_vring_enable(hdev, 0);
-    }
-
     vhost_log_put(hdev, true);
     hdev->started = false;
     hdev->log = NULL;