MQTT reconnect delay based on last disconnection

code/espurna/mqtt.ino

@@ -51,6 +51,7 @@ char *_mqtt_clientid;
 #if MQTT_SKIP_RETAINED
 unsigned long _mqtt_connected_at = 0;
 #endif
+unsigned long _mqtt_disconnected_at = 0;
 
 std::vector<mqtt_callback_f> _mqtt_callbacks;
 
@@ -75,9 +76,7 @@ void _mqttConnect() {
     if (_mqtt.connected()) return;
 
     // Check reconnect interval
-    static unsigned long last = 0;
-    if (millis() - last < _mqtt_reconnect_delay) return;
-    last = millis();
+    if (millis() - _mqtt_disconnected_at < _mqtt_reconnect_delay) return;
 
     // Increase the reconnect delay
     _mqtt_reconnect_delay += MQTT_RECONNECT_DELAY_STEP;
@@ -414,6 +413,8 @@ void _mqttOnConnect() {
 
 void _mqttOnDisconnect() {
 
+    _mqtt_disconnected_at = millis();
+
     DEBUG_MSG_P(PSTR("[MQTT] Disconnected!\n"));
 
     // Send disconnect event to subscribers