Allow TetherService to take a callback to receiver provision results.

See ag/850685 for corresponding framework changes. This is being done
as part of exposing a cleaner tethering API which will be used by
Quick Settings and Settings.

BUG: 26247383
Change-Id: I061b8b8b2b0c5bbe98f50deb051e2bfb8e773d61
3 files changed