drm/doc: add warning about connector_type_id stability

Mention that the connector_type_id is not stable: it depends on
driver and device probe order.

Signed-off-by: Simon Ser <contact@emersion.fr>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20230717131305.616855-1-contact@emersion.fr

include/uapi/drm/drm_mode.h

@@ -488,6 +488,9 @@ struct drm_mode_get_connector {
 	 * This is not an object ID. This is a per-type connector number. Each
 	 * (type, type_id) combination is unique across all connectors of a DRM
 	 * device.
+	 *
+	 * The (type, type_id) combination is not a stable identifier: the
+	 * type_id can change depending on the driver probe order.
 	 */
 	__u32 connector_type_id;