Hotspots with invalid beacons (GatewayNoValidWitnesses) still count as active for HIP17 calculations

[riobah]

Example hotspot: Raspy Holographic Squirrel

• Its txScale is 0.5 (according to the beacon reports in the PoC messages)
• Its closest neighbor hotspot is Cold Cornflower Crow but it has no valid beacons for days.