Add: allow setting your server visibility to "invite-only" (#9434)

In this mode you do register to the Game Coordinator, but your
server will not show up in the public server listing. You can give
your friends the invite code of the server with which they can
join.

src/network/network_func.h

@@ -39,6 +39,7 @@ bool NetworkValidateOurClientName();
 bool NetworkValidateClientName(std::string &client_name);
 bool NetworkValidateServerName(std::string &server_name);
 void NetworkUpdateClientName(const std::string &client_name);
+void NetworkUpdateServerGameType();
 bool NetworkCompanyHasClients(CompanyID company);
 std::string NetworkChangeCompanyPassword(CompanyID company_id, std::string password);
 void NetworkReboot();