api: add has_video attribute to incoming call events

This allows UI to show if incoming call is a video or audio call
and disable camera by default for audio calls.

deltachat-ffi/deltachat.h

@@ -6732,6 +6732,7 @@ void dc_event_unref(dc_event_t* event);
  *
  * @param data1 (int) msg_id ID of the message referring to the call.
  * @param data2 (char*) place_call_info, text passed to dc_place_outgoing_call()
+ * @param data2 (int) 1 if incoming call is a video call, 0 otherwise
  */
 #define DC_EVENT_INCOMING_CALL                            2550