Better treatment of invalid commands --> decreasing risk of getting stuck in the bootloader

[NightHawk32]

Especially when using DShot bidir I found the following scenario happening sometimes:

• Pulling the signal line high (due to passthrough) --> ESC jumps to bootloader
• Reading and changing settings works fine
• switching to "normal" operation with the flight controller sending DSHot commands --> ESC is stuck

The bootloaders sometimes picks up DShot Bidir commands up as commands 0xFF ("CMD_SET_ADDRESS"). With invalid CRC of course. But nevertheless invalid command is never increased (since 0xFF is a valid command) and the ESC is stuck in the bootloader.

Solution:
So when we increase invalid_command whenevver we have bad CRC or unknown commands, we reduce the risk of being stuck in the bootloader and waiting for commands. As soon as we receive a valid command we set invalid_command to 0.

[tridge]

this seems sensible to me - @AlkaMotors ?

[tridge]

@NightHawk32 what FC are you using? Is this betaflight? ArduPilot? PX4?

[NightHawk32]

@tridge tested with rotorflight and betaflight