Send tethered interface callbacks based on interface existence. am: 149860a426 am: cad2e49acb am: cc72f440b1

Change-Id: Iac66c95f07fe81d5c9e1b5dfcd42fe676ea2bc70
tree: 383b74744be1be63e8bd7e62b7fb70b52491a1a5
  1. service-t/
  2. tests/