vhost: fix the fd leak

When the vhost-user reconnect to the backend, the notifer should be
cleanup. Otherwise, the fd resource will be exhausted.

Fixes: f9a09ca ("vhost: add support for configure interrupt")

Signed-off-by: Li Feng <fengli@smartx.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <20230731121018.2856310-2-fengli@smartx.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Fiona Ebner <f.ebner@proxmox.com>

hw/virtio/vhost.c

@@ -2044,6 +2044,8 @@ void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings)
     event_notifier_test_and_clear(
         &hdev->vqs[VHOST_QUEUE_NUM_CONFIG_INR].masked_config_notifier);
     event_notifier_test_and_clear(&vdev->config_notifier);
+    event_notifier_cleanup(
+        &hdev->vqs[VHOST_QUEUE_NUM_CONFIG_INR].masked_config_notifier);
 
     trace_vhost_dev_stop(hdev, vdev->name, vrings);