Status bitmask error

[jku]

As I mentioned in #8 I haven't actually executed this code... but there seems to be a bug in the protocol header parsing in parse_header():

    frame_id = (header >> 5) & 3
    endpoint = (header >> 3) & 3
    status = (header >> 2) & 3
    length = header & 3

status uses two bits here, it looks like it should use only one based on https://dev.tillitis.se/protocol/#response-frame-format:

    status = (header >> 2) & 1

[kchr]

Thank you for the report! I will investigate your proposed change and any potential side effects.