Fix EthernetTetheringTest flaky

The tracking interface of EthernetTracker(mTetheringInterface) is
stopped to track only when it is removed. There is race condition in
EthernetTetheringTest that the new test start ethernet tethering with
previous test interface name because EthernetTracker still tracking
previous test interface.
Destroy test interface then listen untether callback without calling
stopTethering. If EthernetTracker stop tracking test interface, it would
call onUnavailable callback to stop tethering. So the test can check
whether tethering is stopped to ensure the test interface is not tracked
anymore before test finish.

Bug: 191826409
Bug: 243222655
Test: atest TetheringIntegrationTests

Change-Id: I618983d981cd3a707dcb7723cdbb20ba5bf8bd2e

Tethering/tests/integration/src/android/net/EthernetTetheringTest.java

@@ -215,26 +215,26 @@ public class EthernetTetheringTest {
             mUpstreamReader = null;
         }
 
-        runAsShell(TETHER_PRIVILEGED, () -> {
-            mTm.stopTethering(TETHERING_ETHERNET);
-            // Binder call is an async call. Need to hold the shell permission until tethering
-            // stopped. This helps to avoid the test become flaky.
-            if (mTetheringEventCallback != null) {
-                mTetheringEventCallback.awaitInterfaceUntethered();
-                mTetheringEventCallback.unregister();
-                mTetheringEventCallback = null;
-            }
-        });
         if (mDownstreamReader != null) {
             TapPacketReader reader = mDownstreamReader;
             mHandler.post(() -> reader.stop());
             mDownstreamReader = null;
         }
-        runAsShell(NETWORK_SETTINGS, () -> {
+
-            mTetheredInterfaceRequester.release();
+        // To avoid flaky which caused by the next test started but the previous interface is not
-        });
+        // untracked from EthernetTracker yet. Just delete the test interface without explicitly
-        setIncludeTestInterfaces(false);
+        // calling TetheringManager#stopTethering could let EthernetTracker untrack the test
+        // interface from server mode before tethering stopped. Thus, awaitInterfaceUntethered
+        // could not only make sure tethering is stopped but also guarantee the test interface is
+        // untracked from EthernetTracker.
         maybeDeleteTestInterface();
+        if (mTetheringEventCallback != null) {
+            mTetheringEventCallback.awaitInterfaceUntethered();
+            mTetheringEventCallback.unregister();
+            mTetheringEventCallback = null;
+        }
+        runAsShell(NETWORK_SETTINGS, () -> mTetheredInterfaceRequester.release());
+        setIncludeTestInterfaces(false);
     }
 
     @After