[broker] Implements ConvertToTXPK method
[broker] Implements ConvertToTXPK method

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