Fix JSON download interrupted by CAN mapping request

[Modellfan]

Summary

• defer initial CAN mapping load until parameter JSON has loaded successfully
• reject CAN mapping reads while the CAN/JSON state machine is busy
• restart JSON re-download correctly after an invalid cached JSON file
• reset the segmented SDO toggle bit before starting a new JSON download

Testing

• Tested on STM32 VCU hardware
• platformio run succeeds

[jsphuebner]

Just wondering how to handle the conflict between START and CLEAR. The start command is already out there in forms of inverter firmware 5.39.R. So issuing a clear command would in fact start the inverter.
We could just move clear to subIndex 6 to avoid this and mark 4 and 5 as reserved in the source

[Modellfan]

jsphuebner/libopeninv@304ff90

Nothing more is what I did here.

[jsphuebner]

ah, lost that. Please PR (again?)

[Modellfan]

Done. Is reopened. We should fix it here also again. I think I did it already somewhere. Can we merge this PR first, so I don't get to much chaos?

[Modellfan]

I just commited it here.

[Modellfan]

I don't get, how 8948c80
can be still part of this PR . You merged it already twice. Am I doing anything wrong?