Tracking mobility changes

We should check which network clients changed their AP association. This could be done by tracking which client MAC addresses correspond to which BSSID at the `Sniffer` level and detect events such as:
- FT handshake with a mobility zone change
- Just reassociating within the same ESS (no FT handshake)
- Sending encrypted data frames to another BSSID, indicating a missed AP transition cue