Add support for live data subscription via Device::subscribeLiveData() and
Device::unsubscribeLiveData(). The live data API can be used to subscribe to
individual "signals", a full list of which can be found in LiveDataValueType.
The following fixups were added during the squash/merge:
Fix formatting in EthPhyMessage and EthPhyRegPacket
Device: Use std::make_shared when creating the EthPHYControl filter
Network: Create NetID String for EthPHYControl
EthPhyRegPacket: Constants in PascalCase