// lwIP-v2 backlog facility allows to keep memory safe by limiting the// maximum number of incoming *pending clients*.  Default number of possibly// simultaneously pending clients is defined in WiFiServer.cpp// (MAX_PENDING_CLIENTS_PER_PORT=5).  User can overide it at runtime from// sketch://      WiFiServer::begin(port, max-simultaneous-pending-clients);//// An "incoming pending" client is a new incoming TCP connection trying to// reach the TCP server.  It is "pending" until lwIP acknowledges it and// "accepted / no more pending" when user calls WiFiServer::available().//// Before the backlog feature or with lwIP-v1.4, there was no pending// connections: They were immediately accepted and filling RAM.//// Several pending clients can appear during the time when one client is// served by a long not-async service like ESP8266WebServer.  During that// time WiFiServer::available() cannot be called.//// Note: This *does not limit* the number of *simultaneously accepted//       clients*.  Such limit management is left to the user.//// Thus, when the maximum number of pending connections is reached, new// connections are delayed.// By "delayed", it is meant that WiFiServer(lwIP) will not answer to the// SYN packet until there is room for a new one: The TCP server on that port// will be mute.  The TCP client will regularly try to connect until success// or a timeout occurs (72s on windows).//// When user calls WiFiServer::available(), the tcp server stops muting and// answers to newcomers (until the "backlog" pending list is full again).