[trivial] Add end of namespace comments

src/protocol.cpp

@@ -39,7 +39,7 @@ const char *SENDCMPCT="sendcmpct";
 const char *CMPCTBLOCK="cmpctblock";
 const char *GETBLOCKTXN="getblocktxn";
 const char *BLOCKTXN="blocktxn";
-};
+} // namespace NetMsgType
 
 /** All known message types. Keep this in the same order as the list of
  * messages above and in protocol.h.