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

Merged-In: I34842acd94b972e440c3622f7617df10c18acf65
Change-Id: I34842acd94b972e440c3622f7617df10c18acf65
(cherry-pick with conflicts in test-current.txt)
diff --git a/Tethering/tests/unit/AndroidManifest.xml b/Tethering/tests/unit/AndroidManifest.xml
index 0a1cdd3..530bc07 100644
--- a/Tethering/tests/unit/AndroidManifest.xml
+++ b/Tethering/tests/unit/AndroidManifest.xml
@@ -16,6 +16,8 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
           package="com.android.networkstack.tethering.tests.unit">
 
+    <uses-permission android:name="android.permission.TETHER_PRIVILEGED"/>
+
     <application android:debuggable="true">
         <uses-library android:name="android.test.runner" />
     </application>