Replace ConnectivityManager hidden symbols on SettingsLib

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 SettingsLib.

Bug: 180693313
Test: atest SettingsLibRoboTests
Change-Id: I11e317ed0d3aab2628082bbe6b8292fec82109a9