ClientInterface: add a function to verify (correctly) if user limit was reached (#6258)

* ClientInterface: add a function to verify (correctly) if user limit was reached

CS_HelloSent is a better indicator of active slots than CS_Created, which are session objects created after init packet reception

Switch existing checks to ClientInterface::isUserLimitReached()

Use range-based for loop for getClientIds() used function too

This will fix #6254 (not the memory overhead if init is flooded)

src/clientiface.h

@@ -427,6 +427,9 @@ public:
 	/* get list of active client id's */
 	std::vector<u16> getClientIDs(ClientState min_state=CS_Active);
 
+	/* verify is server user limit was reached */
+	bool isUserLimitReached();
+
 	/* get list of client player names */
 	const std::vector<std::string> &getPlayerNames() const { return m_clients_names; }
 
@@ -472,7 +475,6 @@ public:
 	}
 
 	static std::string state2Name(ClientState state);
-
 protected:
 	//TODO find way to avoid this functions
 	void lock() { m_clients_mutex.lock(); }