Fix CAN filtering to allow mask matching

[heliochronix]

Currently, CAN filtering implements a per-message-ID filtering scheme in order to maximize the available number of filters that can be used. However, in the case of CANopen Emergency Messages, we need to have at least one message mask filter in place to match all 0x80+NodeID messages. Right now the C3 card can't receive Emergency messages due to this issue.

The challenge is, the index of the CAN filter acts as the index into the internal CANopenNode buffer in order to process the message. We need to find a way that ensures the index remains correct.