fixes tlm_managed_extension inheritance

Author: eyck

src/sysc/tlm/scc/tlm_extensions.h

@@ -43,7 +43,7 @@ template <typename T> struct tlm_unmanaged_extension : public tlm_extension<T> {
     void copy_from(tlm_extension_base const& other) override { this->operator=(static_cast<const type&>(other)); }
 
 protected:
-    tlm_unmanaged_extension(){};
+    tlm_unmanaged_extension() {};
 };
 /*!
  * \brief A managed extension for TLM transactions.
@@ -52,7 +52,7 @@ template <typename T> struct tlm_unmanaged_extension : public tlm_extension<T> {
  *
  * \tparam T The type of the extension.
  */
-template <typename T> struct tlm_managed_extension {
+template <typename T> struct tlm_managed_extension : public tlm_extension<T> {
 
     using type = T;