Fix MDNS in IRServer and IRMQTTServer (#1499)

Fix MDNS service in IRServer and IRMQTTServer examples

In the examples IRServer and IRMQTTServer, Chromium and Firefox running on Ubuntu fail to connect to the ESP8266 using the MDNS hostname. For example, esp8266.local and ir_server.local do not resolve.

Based on the MDNS examples included with the ESP8266 board package, adding calls to mdns.addService() and mdns.update() fixes the problems.

Fixes #1498

examples/IRMQTTServer/IRMQTTServer.ino

@@ -2143,6 +2143,8 @@ void setup(void) {
   if (mdns.begin(Hostname)) {
 #endif  // ESP8266
     debug("MDNS responder started");
+    // Announce http tcp service on kHttpPort
+    mdns.addService("http", "tcp", kHttpPort);
   }
 #endif  // MDNS_ENABLE
 
@@ -2591,6 +2593,9 @@ void sendMQTTDiscovery(const char *topic) {
 #endif  // MQTT_ENABLE
 
 void loop(void) {
+#if MDNS_ENABLE && defined(ESP8266)
+  mdns.update();
+#endif  // MDNS_ENABLE and ESP8266
   server.handleClient();  // Handle any web activity
 
 #if MQTT_ENABLE

examples/IRServer/IRServer.ino

@@ -132,6 +132,8 @@ void setup(void) {
   if (mdns.begin(HOSTNAME)) {
 #endif  // ESP8266
     Serial.println("MDNS responder started");
+    // Announce http tcp service on port 80
+    mdns.addService("http", "tcp", 80);
   }
 
   server.on("/", handleRoot);
@@ -148,5 +150,8 @@ void setup(void) {
 }
 
 void loop(void) {
+#if defined(ESP8266)
+  mdns.update();
+#endif
   server.handleClient();
 }