Packet ID doesn't work

[llamafilm]

How is packet_id meant to be used? It seems broken but maybe I'm missing something.

>>> from bthome import BTHome
>>> beacon = BTHome()
>>> beacon.packet_id
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "bthome.py", line 310, in packet_id
AttributeError: 'BTHome' object has no attribute '_packet_id'

I think we just need to add self._packet_id = 0 to the class constructor. After doing that, it increments on each advertisement.

[DavesCodeMusings]

Going with self._packet_id = -1 so it will increment to 0 on first use.

[DavesCodeMusings]

Added self._packet_id = -1 to class constructor. Should be fixed. Please give it a test and let me know.

[llamafilm]

Looks OK to me