/sim/multiplay/protocol-version is either 1 or 2
The properties defined in multiplaymgr define which version they are related to; however if these are in a more recent protocol than selected they will be transmitted in the selected protocol version.
The id property list now defines a "transmit as" - however this is not yet implemented.
This commit is intended to be a WIP towards changes for 2017.1 that will ensure any future protocol changes are compatible with this version (so this 2017.1 would be able to see a protocl V3 FG if one ever existed), key to this is to stop processing the property list as soon as an unknown ID is encountered.