Modify SettingsLib for partial connectivity

Add partial connectivity related settings in SettingsLib.

Bug: 113450764
Bug: 128489091
Test: 1. Build pass.
      2. Fake partial connectivity case for testing.

Change-Id: I0733ecc9070e6c4281fdff40f432605d139355ec
Merged-In: I4791abe9351c62d9549ada383aa4cc8aa34ddaf2