[test-router] Fix small issues in Register() method according to test results
[test-router] Fix small issues in Register() method according to test results

TheThingsNetwork/ttn,mgranberry/ttn,jvanmalder/ttn,jvanmalder/ttn,jvanmalder/ttn,TheThingsNetwork/ttn,TheThingsNetwork/ttn,LoRaWanSoFa/ttn,mgranberry/ttn,LoRaWanSoFa/ttn,mgranberry/ttn