Implement BlockAckManager::DoDispose ()

Nullify all Ptr's there to remove possible circular references.

Do not set m_queue Ptr in the destructor, it is destroyed anyway.

src/wifi/model/block-ack-manager.cc

@@ -72,9 +72,17 @@ BlockAckManager::BlockAckManager ()
 BlockAckManager::~BlockAckManager ()
 {
   NS_LOG_FUNCTION (this);
-  m_queue = 0;
+}
+
+void
+BlockAckManager::DoDispose ()
+{
+  NS_LOG_FUNCTION (this);
   m_agreements.clear ();
-  m_retryPackets = 0;
+  m_retryPackets = nullptr;
+  m_bars.clear ();
+  m_queue = nullptr;
+  m_stationManager = nullptr;
 }
 
 bool

src/wifi/model/block-ack-manager.h

@@ -431,6 +431,9 @@ public:
    */
   void ScheduleBar (Ptr<const WifiMacQueueItem> bar, bool skipIfNoDataQueued = false);
 
+protected:
+  void DoDispose () override;
+
 private:
   /**
    * Inactivity timeout function