Automatically set mqtt buffer size (#637)

* Automatically set mqtt buffer size

Current versions of pubsubclient allows the buffer size to be set
dynamically: https://github.com/knolleary/pubsubclient/pull/282

We can take advantage of this to avoid having to modify one of the
dependencies and instead automatically up the buffer size when a
powerful board is detected.

main/main.ino

@@ -401,6 +401,7 @@ void connectMQTT() {
   char topic[mqtt_topic_max_size];
   strcpy(topic, mqtt_topic);
   strcat(topic, will_Topic);
+  client.setBufferSize(mqtt_max_packet_size);
   if (client.connect(gateway_name, mqtt_user, mqtt_pass, topic, will_QoS, will_Retain, will_Message)) {
 #if defined(ZboardM5STICKC) || defined(ZboardM5STACK)
     if (low_power_mode < 2)
@@ -604,11 +605,7 @@ void setup() {
 #ifdef ZsensorDHT
   setupDHT();
 #endif
-  Log.trace(F("MQTT_MAX_PACKET_SIZE: %d" CR), MQTT_MAX_PACKET_SIZE);
-#if defined(ESP8266) || defined(ESP32) || defined(__AVR_ATmega2560__) || defined(__AVR_ATmega1280__)
-  if (MQTT_MAX_PACKET_SIZE == 128)
-    Log.error(F("WRONG PUBSUBCLIENT LIBRARY USED PLEASE INSTALL THE ONE FROM RELEASE PAGE" CR));
-#endif
+  Log.trace(F("mqtt_max_packet_size: %d" CR), mqtt_max_packet_size);
   Log.notice(F("Setup OpenMQTTGateway end" CR));
 }