lwIP on ethernet: examples (#8395)

* ethernet: examples

* remove duplicate

* styling

* fix comment restyle + comment eth.setdefault()

* comment and add comments about eth.setDefault()

* update comments when using interface::setDefault()

* repair bad merge

* fix default interface case

* factorize

* change comment

libraries/lwIP_w5500/examples/TCPClient/TCPClient.ino

@@ -1,91 +0,0 @@
-/*
-    This sketch establishes a TCP connection to a "quote of the day" service.
-    It sends a "hello" message, and then prints received data.
-*/
-
-#include <SPI.h>
-#include <W5500lwIP.h>
-// or #include <W5100lwIP.h>
-// or #include <ENC28J60lwIP.h>
-
-#include <WiFiClient.h>  // WiFiClient (-> TCPClient)
-
-const char* host = "djxmmx.net";
-const uint16_t port = 17;
-
-using TCPClient = WiFiClient;
-
-#define CSPIN 16  // wemos/lolin/nodemcu D0
-Wiznet5500lwIP eth(CSPIN);
-
-void setup() {
-  Serial.begin(115200);
-
-  SPI.begin();
-  SPI.setClockDivider(SPI_CLOCK_DIV4);  // 4 MHz?
-  SPI.setBitOrder(MSBFIRST);
-  SPI.setDataMode(SPI_MODE0);
-  eth.setDefault();  // use ethernet for default route
-  if (!eth.begin()) {
-    Serial.println("ethernet hardware not found ... sleeping");
-    while (1) { delay(1000); }
-  } else {
-    Serial.print("connecting ethernet");
-    while (!eth.connected()) {
-      Serial.print(".");
-      delay(1000);
-    }
-  }
-  Serial.println();
-  Serial.print("ethernet IP address: ");
-  Serial.println(eth.localIP());
-}
-
-void loop() {
-  static bool wait = false;
-
-  Serial.print("connecting to ");
-  Serial.print(host);
-  Serial.print(':');
-  Serial.println(port);
-
-  TCPClient client;
-  if (!client.connect(host, port)) {
-    Serial.println("connection failed");
-    delay(5000);
-    return;
-  }
-
-  // This will send a string to the server
-  Serial.println("sending data to server");
-  if (client.connected()) { client.println("hello from ESP8266"); }
-
-  // wait for data to be available
-  unsigned long timeout = millis();
-  while (client.available() == 0) {
-    if (millis() - timeout > 5000) {
-      Serial.println(">>> Client Timeout !");
-      client.stop();
-      delay(60000);
-      return;
-    }
-  }
-
-  // Read all the lines of the reply from server and print them to Serial
-  Serial.println("receiving from remote server");
-  // not testing 'client.connected()' since we do not need to send data here
-  while (client.available()) {
-    char ch = static_cast<char>(client.read());
-    Serial.print(ch);
-  }
-
-  // Close the connection
-  Serial.println();
-  Serial.println("closing connection");
-  client.stop();
-
-  if (wait) {
-    delay(300000);  // execute once every 5 minutes, don't flood remote service
-  }
-  wait = true;
-}