Set the callback for the `self_connection_status` event. Pass NULL to unset.
This event is triggered whenever there is a change in the DHT connection state. When disconnected, a client may choose to call Tox.bootstrap again, to reconnect to the DHT. Note that this state may frequently change for short amounts of time. Clients should therefore not immediately bootstrap on receiving a disconnect.
TODO(iphydf): how long should a client wait before bootstrapping again?