wifi data usage: Query wifi usage per configuration

- Updated to use the AllNetworkKeys set instead of NetworkId.

- Fix crash issue when mDataUsageController is not created.

- See b/126299427#comment37 for a screenshot.

Bug: 126299427
Test: manual test
make RunSettingsRoboTests
ROBOTEST_FILTER=DataUsageSummaryPreferenceControllerTest
make RunSettingsRoboTests
ROBOTEST_FILTER=WifiDetailPreferenceController2Test
make RunSettingsRoboTests
ROBOTEST_FILTER=WifiDataUsageSummaryPreferenceControllerTest

Change-Id: I26289fde1f18d97631448edc71e034d33b865cc4