[hotfix] stats mutex
[hotfix] stats mutex

Was introduced in 4132e8dd

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