Make carrier offloading shared settings

- Move carrier Wifi offloding setting to shared store.
- Keep IMSI protection examption user approval info in user specific
store

This will result in S dogfooders losing both IMSI and carrier offloading
info. But end users updating from R to S will not be affected.

Bug: 176004489
Test: atest FrameworksWifiTests

Change-Id: I134a443541c788dc3874380eaddcd06d362b5421
8 files changed