RTSPWatch.sendMessages

Sends messages using the connection of the watch. If they cannot be sent immediately, they will be queued for transmission in watch. The contents of messages will then be serialized and transmitted when the connection of the watch becomes writable. In case the messages are queued, the ID returned in id will be non-zero and used as the ID argument in the message_sent callback once the last message is sent. The callback will only be called once for the last message.