IOConnection: Add a callback before data is sent

[nefethael]

This allows to refresh current output assembly buffer before it is sent, for example this way

            ptr->setSendDataListener(
                    [this, id](auto& data)
                        {
                            std::unique_lock<std::mutex> lock(_mutex);
                            data = _map[id].GetBytes();
                        }
            );

Signed-off-by: Vincent Prince vincent.prince.external@saftbatteries.com

[atimin]

Good idea! Thank you!