Add support for Ethernet tethering

Ethernet tethering can be started via
startTethering(TETHERING_ETHERNET).

Test: flashed, enabled ethernet tethering, verified internet access on
      downstream.
Bug: 130840861

Change-Id: I34842acd94b972e440c3622f7617df10c18acf65
diff --git a/Tethering/tests/unit/Android.bp b/Tethering/tests/unit/Android.bp
index 53782fe..13174c5 100644
--- a/Tethering/tests/unit/Android.bp
+++ b/Tethering/tests/unit/Android.bp
@@ -19,6 +19,7 @@
     certificate: "platform",
     srcs: [
         "src/**/*.java",
+        "src/**/*.kt",
     ],
     test_suites: [
         "device-tests",