Feature: add support for `GS_CAN_FEATURE_GET_STATE` and `GS_CAN_FEATURE_BERR_REPORTING`

In this issue I want to track implementation of the GS_CAN_FEATURE_GET_STATE and GS_CAN_FEATURE_BERR_REPORTING features.

@jhofstee, do you have some work-in-progress code somewhere? Is the newest code in this branch? https://github.com/jhofstee/candleLight_fw/tree/canbus-state

As far as I can see in #107 and #119 the error frame generation was cleaned up. I want to make sure that this is merged and no code was forgotten.

In #124 (comment) @jhofstee says his implementation can be rebased to mainline.

FTR: The new features have been documented in #124.

Linux support has been mainlined with torvalds/linux@0c9f92a

I wonder if this could be extended to count dropped frames (RX overflows) ...

We already have the GS_CAN_FLAG_OVERFLOW to signal a RX overflow to Linux:

Line 83 in 4a1e646

#define GS_CAN_FLAG_OVERFLOW (1<<0)

It's not used in the candlelight FW, though.