Show "Not available" summary when hotspot speed is unavailable

- Show "Not available" summary when hotspot bands (5 GHz and 6 GHz) are unavailable

- Update debug logs to track down issues

Bug: 285769583
Test: manual test
atest -c WifiHotspotSpeedSettingsTest
atest -c WifiHotspotSpeedViewModelTest

Change-Id: If1050c120b4b612d3a9adbe886c2f12db82b793e