Add a device config for actively preferring bad wifi

Test: FrameworksNetTests
      adb shell device_config put connectivity actively_prefer_bad_wifi
       + check that dumpsys updates
Test: at this patchset tests fail with :
      Permission denial: reading from settings requires:android.permission.READ_DEVICE_CONFIG

Change-Id: Icfe1e64b8313921ff1dc8e4cbd45f967692e1c4a