Fix testUpdateConnectedClientsForLocalOnlyHotspot

testUpdateConnectedClientsForLocalOnlyHotspot should not run before T,
but it don't be ignored correctly because missing DevSdkIgnoreRule
setup.

Bug: 233077722
Test: TH
Change-Id: Ib2d241f927ccdc5d2bc392962481ecb86a223e09
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringTest.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringTest.java
index 80666e6..773cae3 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringTest.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringTest.java
@@ -195,12 +195,14 @@
 import com.android.networkstack.apishim.common.UnsupportedApiLevelException;
 import com.android.networkstack.tethering.TestConnectivityManager.TestNetworkAgent;
 import com.android.networkstack.tethering.metrics.TetheringMetrics;
+import com.android.testutils.DevSdkIgnoreRule;
 import com.android.testutils.DevSdkIgnoreRule.IgnoreUpTo;
 import com.android.testutils.MiscAsserts;
 
 import org.junit.After;
 import org.junit.Before;
 import org.junit.BeforeClass;
+import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.ArgumentCaptor;
@@ -223,6 +225,8 @@
 @RunWith(AndroidJUnit4.class)
 @SmallTest
 public class TetheringTest {
+    @Rule public final DevSdkIgnoreRule mIgnoreRule = new DevSdkIgnoreRule();
+
     private static final int IFINDEX_OFFSET = 100;
 
     private static final String TEST_MOBILE_IFNAME = "test_rmnet_data0";