[Settings] Replace CONNECTIVITY_INTERNAL to TETHER_PRIVILEGED

Settings is using CONNECTIVITY_INTERNAL to restrict launching
tether provisoning activity by provioning apps only. However,
CONNECTIVITY_INTERNAL will be deprecated from Android R, replace
the permission to TETHER_PRIVILEGED.

Bug: 32963470
Test: atest TetherServiceTest
Change-Id: I4c8312b92de8d5d9c9090c572e54622dc4fcf9d4