* Add a listener in order to be notified of LinphoneChatRoom events. Once an event is received, registred LinphoneChatRoomCbs are
* invoked sequencially.
* @param[in] call LinphoneChatRoom object to monitor.
* @param[in] cbs A LinphoneChatRoomCbs object holding the callbacks you need. A reference is taken by the LinphoneChatRoom until you invoke linphone_call_remove_callbacks().
* This is meant only to be called from a callback to be able to get the user_data associated with the LinphoneChatRoomCbs that is calling the callback.
* @param[in] call LinphoneChatRoom object
* @return The LinphoneChatRoomCbs that has called the last callback