spectrum: Add getters for propagation loss models

src/spectrum/model/phased-array-spectrum-propagation-loss-model.cc

@@ -60,6 +60,12 @@ PhasedArraySpectrumPropagationLossModel::SetNext(Ptr<PhasedArraySpectrumPropagat
     m_next = next;
 }
 
+Ptr<PhasedArraySpectrumPropagationLossModel>
+PhasedArraySpectrumPropagationLossModel::GetNext() const
+{
+    return m_next;
+}
+
 Ptr<SpectrumSignalParameters>
 PhasedArraySpectrumPropagationLossModel::CalcRxPowerSpectralDensity(
     Ptr<const SpectrumSignalParameters> params,

src/spectrum/model/phased-array-spectrum-propagation-loss-model.h

@@ -61,6 +61,13 @@ class PhasedArraySpectrumPropagationLossModel : public Object
      */
     void SetNext(Ptr<PhasedArraySpectrumPropagationLossModel> next);
 
+    /**
+     * Return the pointer to the next PhasedArraySpectrumPropagationLossModel, if any.
+     *
+     * @return Pointer to the next model, if any
+     */
+    Ptr<PhasedArraySpectrumPropagationLossModel> GetNext() const;
+
     /**
      * This method is to be called to calculate
      *

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

@@ -59,6 +59,12 @@ SpectrumPropagationLossModel::SetNext(Ptr<SpectrumPropagationLossModel> next)
     m_next = next;
 }
 
+Ptr<SpectrumPropagationLossModel>
+SpectrumPropagationLossModel::GetNext() const
+{
+    return m_next;
+}
+
 Ptr<SpectrumValue>
 SpectrumPropagationLossModel::CalcRxPowerSpectralDensity(Ptr<const SpectrumSignalParameters> params,
                                                          Ptr<const MobilityModel> a,

src/spectrum/model/spectrum-propagation-loss-model.h

@@ -59,6 +59,13 @@ class SpectrumPropagationLossModel : public Object
      */
     void SetNext(Ptr<SpectrumPropagationLossModel> next);
 
+    /**
+     * Return the pointer to the next SpectrumPropagationLossModel, if any.
+     *
+     * @return Pointer to the next model, if any.
+     */
+    Ptr<SpectrumPropagationLossModel> GetNext() const;
+
     /**
      * This method is to be called to calculate
      *