Smart Router settings UI changes

- Remove "AP band" preference

- Add "Maximize Compatibility" switch preference
  - Use bridged mode API for new devices (after P21)

- Screenshot:
  https://screenshot.googleplex.com/84X9Av8gVj3idjB

Bug: 168052744
Test: manual test
atest WifiTetherMaximizeCompatibilityPreferenceControllerTest
make RunSettingsRoboTests ROBOTEST_FILTER=WifiTetherSettingsTest

Change-Id: Ib74156c0fa6eccdd13239854047b1fb4e49a293c