Set up the jarjar config generator for the Tethering module.

This does not affect existing classes in framework-tethering.jar
as everything inside android.net is excluded from being jarjar'ed.
It is a preparatory step to adding cronet to framework-tethering.jar
which will use jarjar.

Test: m
Change-Id: I8cc7babaa37f7aef52306a833593dba097fd26db
3 files changed