[WifiTrackerLib] Distinguish entries with same BSSID but different SSIDs

Currently, scan results are merged by BSSID in the wifi tracker,
resulting in one entry being shown if there are two SSIDs advertised
with the same BSSID. This change merges scan results by SSID+BSSID pair
to avoid this case.

Test: atest WifiTrackerLibTests
Bug: 160544965
Change-Id: I0ec29335197759e9c28a6486b869845e85bb74d2
2 files changed