include: attempt to document device_class_set_props

I'm still not sure how I achieve by use case of the parent class
defining the following properties:

  static Property vud_properties[] = {
      DEFINE_PROP_CHR("chardev", VHostUserDevice, chardev),
      DEFINE_PROP_UINT16("id", VHostUserDevice, id, 0),
      DEFINE_PROP_UINT32("num_vqs", VHostUserDevice, num_vqs, 1),
      DEFINE_PROP_END_OF_LIST(),
  };

But for the specialisation of the class I want the id to default to
the actual device id, e.g.:

  static Property vu_rng_properties[] = {
      DEFINE_PROP_UINT16("id", VHostUserDevice, id, VIRTIO_ID_RNG),
      DEFINE_PROP_UINT32("num_vqs", VHostUserDevice, num_vqs, 1),
      DEFINE_PROP_END_OF_LIST(),
  };

And so far the API for doing that isn't super clear.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230710153522.3469097-2-alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/hw/qdev-core.h

@@ -926,6 +926,15 @@ BusState *sysbus_get_default(void);
 char *qdev_get_fw_dev_path(DeviceState *dev);
 char *qdev_get_own_fw_dev_path_from_handler(BusState *bus, DeviceState *dev);
 
+/**
+ * device_class_set_props(): add a set of properties to an device
+ * @dc: the parent DeviceClass all devices inherit
+ * @props: an array of properties, terminate by DEFINE_PROP_END_OF_LIST()
+ *
+ * This will add a set of properties to the object. It will fault if
+ * you attempt to add an existing property defined by a parent class.
+ * To modify an inherited property you need to use????
+ */
 void device_class_set_props(DeviceClass *dc, Property *props);
 
 /**