dispose the channel from WifiNetDevice

src/devices/wifi/wifi-net-device.cc

@@ -216,6 +216,14 @@ WifiNetDevice::DoGetChannel (void) const
 {
   return m_channel;
 }
+void 
+WifiNetDevice::DoDispose (void)
+{
+  // chain up.
+  NetDevice::DoDispose ();
+  // cleanup local
+  m_channel = 0;
+}
 
 
 /*****************************************************

src/devices/wifi/wifi-net-device.h

@@ -70,6 +70,7 @@ private:
 protected:
   WifiNetDevice (Ptr<Node> node);
   void DoForwardUp (Packet packet, const Mac48Address &from);
+  virtual void DoDispose (void);
   DcaTxop *CreateDca (uint32_t minCw, uint32_t maxCw) const;
 
   Ptr<WifiChannel> m_channel;