Tolerate bit errors in the PCI value

[argilo]

As noted in #312 (comment), the has_fixed function prevents data from being processed unless the PCI bits match one of the expected values exactly. When signal quality is poor, bits may be corrupted, disabling data decoding.

A couple possible solutions:

• Use fuzzy matching to determine the most likely PCI value.
• In the event of bit errors, assume that the PCI value is equal to the value seen in previous L2 PDUs.