simple_can_simulator: add support for different interface for LIN events

Previously the CAN messages for the LIN events were bridged to the primary CAN interface, but this proved unreliable in practice, and it has been decided to avoid this in the full AGL demo setup if possible to make the demo more robust.  This requires adding support for receiving the CAN messages for the cruise control LIN events from the steering wheel on a different CAN interface, i.e. sllin0 in the demo setup.

Note that one issue with this is that it complicates injecting CAN from an external device, in that situation the steering wheel controls will not make it to the simulator script running on the external device.  Addressing that likely will require building functionality to send CAN messages to a virtual ECU that the simulator can act on to have things work more like a real vehicle.