partial for #681: Never let stale nodeinfos/positions stay in xmit queue

src/mesh/RadioLibInterface.h

@@ -136,6 +136,9 @@ class RadioLibInterface : public RadioInterface, protected concurrency::Notified
      */
     virtual bool isActivelyReceiving() = 0;
 
+    /** Attempt to cancel a previously sent packet.  Returns true if a packet was found we could cancel */
+    virtual bool cancelSending(NodeNum from, PacketId id);
+    
   private:
     /** if we have something waiting to send, start a short random timer so we can come check for collision before actually doing
      * the transmit