Set sdk_version for tethering.proto.

Test: Manual build
Change-Id: Id383dd22b69fcda96440f33b2384854ff472debf
diff --git a/stats/enums/stats/connectivity/Android.bp b/stats/enums/stats/connectivity/Android.bp
index 4579c48..748a7df 100644
--- a/stats/enums/stats/connectivity/Android.bp
+++ b/stats/enums/stats/connectivity/Android.bp
@@ -39,4 +39,5 @@
         "com.android.tethering",
     ],
     sdk_version: "system_current",
+    min_sdk_version: "30",
 }