message: refactor: Use explicit function type instead of template
diff: @@ -261,8 +261,8 @@ public:
  void PushMessage(CNode* pnode, CSerializedNetMsg&& msg);
  - template<typename Callable>
  - void ForEachNode(Callable&& func)
  + using NodeFn = std::function<void(CNode*)>;
  + void ForEachNode(const NodeFn& func)
  {
  LOCK(cs_vNodes);
  for (auto&& node : vNodes) {
  @@ -271,8 +271,7 @@ public:
  }
  };
  - template<typename Callable>
  - void ForEachNode(Callable&& func) const
  + void ForEachNode(const NodeFn& func) const
  {
  LOCK(cs_vNodes);
  for (auto&& node : vNodes) {
  