ConstReadonlyDeviceControlled: LorawanRelayActivationHowever the device itself decides, which EndDevice.useRelay sets.
ReadonlyDisabled: LorawanRelayActivationNever, the default.
ReadonlyDynamic: LorawanRelayActivationOnly once a run of uplinks went unanswered, as the network's smart-enable level sets.
ReadonlyEnabled: LorawanRelayActivationAlways.
How an end device decides whether to send through a relay, TS011-1.0.1 section 10.2.