Make the destructor of the SocketHandler class protected non-virtual

src/network/socket_handler.hpp

@@ -22,9 +22,10 @@ class Poller;
  */
 class SocketHandler
 {
+protected:
+  ~SocketHandler() {}
 public:
   explicit SocketHandler(std::shared_ptr<Poller> poller);
-  virtual ~SocketHandler() {}
   /**
    * Initialize the socket with the parameters contained in the given
    * addrinfo structure.