Codechange: [Network] replace _realtime_tick with std::chrono

(cherry picked from commit 53c28a8ec9)

src/network/network_admin.h

@@ -37,7 +37,7 @@ protected:
 	NetworkRecvStatus SendPong(uint32 d1);
 public:
 	AdminUpdateFrequency update_frequency[ADMIN_UPDATE_END]; ///< Admin requested update intervals.
-	uint32 realtime_connect;                                 ///< Time of connection.
+	std::chrono::steady_clock::time_point connect_time;      ///< Time of connection.
 	NetworkAddress address;                                  ///< Address of the admin.
 
 	ServerNetworkAdminSocketHandler(SOCKET s);