DDS15 — set_listener behavior is underspecified

Suppose the DATA_AVAILABLE StatusChangedFlag (see Figure 2.16) is set on a DataReader and then a listener (with DATA_AVAILABLE_STATUS in its mask) is attached to the DataReader by the user calling set_listener(). The specification does not specify if the listener should be invoked. If the decision is that the listener is not invoked, then guidance should be given to users that they may need to invoke the listener manually.