Add support for ring counter

[spacemanspiff2007]

Shelly blue messages contain a counter which goes from 0 .. 255 and then starts again at 0.
Create an implementation that allows ignoring already processed messages.
Something like that:

        skip_last = 10
        min_nr = self.last_packet - skip_last

        if min_nr <= packet <= self.last_packet:
            return None
        if min_nr < 0 and packet >= 255 + min_nr:
            return None
        self.last_packet = packet