Replace ConnectivityManager hidden symbols on BT

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 to TetheringManager.

Bug: 180693313
Test: atest BluetoothInstrumentationTests:PanServiceTest
Change-Id: I3cda4923adc47e06e6ebc48684bd87ca2acbdb2a