refactor(db): add constante for max QOS

db/src/mqtt/mqtt.go

@@ -14,6 +14,8 @@ import (
 	mqtt "github.com/eclipse/paho.mqtt.golang"
 )
 
+const maxQoS = 2
+
 // A MqttParams is the abstracted MQTT gateway.
 // It provides the MQTT parameters to initialize the connection and the method to add data.
 type MqttParams struct {
@@ -69,7 +71,7 @@ func NewMqttGateway(p MqttParams) (*MqttGateway, error) {
 		return nil, errors.New("[MQTT Gateway] Invalid client id")
 	}
 
-	if p.Qos > 2 {
+	if p.Qos > maxQoS {
 		return nil, errors.New("[MQTT Gateway] Invalid QoS level")
 	}