refactor: s/command/msg_type/ in CNetMsgMaker and CSerializedNetMsg

src/net.h

@@ -108,7 +108,7 @@ struct CSerializedNetMsg
     CSerializedNetMsg& operator=(const CSerializedNetMsg&) = delete;
 
     std::vector<unsigned char> data;
-    std::string command;
+    std::string m_type;
 };