spectrum: Change order of disposal for ThreeGppPropagationLossModel

src/spectrum/model/spectrum-channel.cc

@@ -33,9 +33,18 @@ void
 SpectrumChannel::DoDispose()
 {
     NS_LOG_FUNCTION(this);
+
+    // Any propagation model that holds a pointer
+    // back to the spectrum channel should not call Dispose()
+    // of its channel pointer, or else a loop may occur.
     m_propagationLoss = nullptr;
     m_propagationDelay = nullptr;
     m_spectrumPropagationLoss = nullptr;
+    if (m_phasedArraySpectrumPropagationLoss)
+    {
+        m_phasedArraySpectrumPropagationLoss->Dispose();
+    }
+    m_phasedArraySpectrumPropagationLoss = nullptr;
 }
 
 TypeId

src/spectrum/model/three-gpp-spectrum-propagation-loss-model.cc

@@ -44,7 +44,6 @@ void
 ThreeGppSpectrumPropagationLossModel::DoDispose()
 {
     m_longTermMap.clear();
-    m_channelModel->Dispose();
     m_channelModel = nullptr;
 }