Move tethering out of ConnectivityService. All client would
use TetheringManager to talk with TetheringService directly.
Bug: 144320246
Test: -build, flash, boot
-atest TetheringTests
Change-Id: Ib051bea724a256f9c4572b566e46ae7b9c4abe6e
Merged-In: Ib051bea724a256f9c4572b566e46ae7b9c4abe6e
Add IpServer which is used to serve ip configuration, dhcp, dns proxy
and nat for downstream interface.
Bug: 136040414
Test: -build, flash, boot
-atest TetheringTests
-atest FrameworksNetTests
Change-Id: I23652ae0b9509abe7d38da96d523eb22ab00a343