Make MSP more robust

[shellixyz]

Make all MSP SET messages read operations safe and add a couple of bound checks.

[digitalentity]

@shellixyz if it's tested - I'm ok with merging it

[fiam]

I’m just a bit worried of the exact size checks. Some buggy client implementation might be sending extra bytes in the payload, which have been harmless until now. With these changes, we might break them. Of course, if we were starting from scratch I’d enforce exact sizes, but at this point I’m not sure if checking for >= would be a better idea.

[digitalentity]

@fiam good point. I'd just ensure we have no less bytes than we need

[stronnag]

No problems with the == diff on mwp or iNav configurator.

[shellixyz]

I tested this while doing normal configuration through the GUI. Not all the messages were tested. Basically all I did was add the dataSize checks so if I calculated the data length of the messages correctly (which I checked twice) it should be good. Does an utility already exist to generate MSP frames that could be used to test all the messages ?

Should I change the conditions to >= or could be keep ==. The benefit of using == is that developers can know when the message data is not right (extraneous data).

[digitalentity]

I think for compatibility reasons it's better to have >=

[shellixyz]

I changed == to >= for the MSPv1 messages. I don't think it makes sense to do it for MSPv2 messages as they have been added only recently and most likely haven't been used anywhere else than in the configurator.