Replace ConnectivityManager hidden symbols on Settings

Connectivity is becoming a mainline module in S, so
ConnectivityManager hidden symbols can not be used for outside
components. Besides, most Tethering relevant methods or variables
on CM are migrated to TetheringManager. So replace all these
methods or variables from ConnectivityManager to TetheringManager
on Settings.

Bug: 180693313
Test: make RunSettingsRoboTests ROBOTEST_FILTER=<Modified Test>
Change-Id: Iba4b121a4ddf3f04252aa0355e0e6494a593682a