pandad: can't use an external panda when you have a missing internal panda

[andiradulescu]

When you have a missing internal panda (most likely because of a hardware problem) and trying to use an external panda with a C3X, pandad keeps printing "Internal panda is missing, trying again" in a loop, not allowing the external panda to connect.

A log can be found here: panda.logs.txt. The problem was spotted on Discord.

I assume the problem can be easily fixed by checking if no_internal_panda_count is over X (where X is the max no of internal panda failures) and let it exit the loop.

As a PoC, commenting out the whole "Internal panda is missing, trying again" check, allows the external panda to connect.

[makifb]

Thank you.

[adeebshihadeh]

This isn't something we intend to support.

If someone puts up a PR, we'll consider it, but it'll likely be too complex to accept.