ITetheredInterfaceCallback is a oneway interface

This is sent from the system server, and the system server doesn't like
being blocked by apps.

Change-Id: I603be3038831974baf1dc392ff0d062e9db91b63
Test: atest CtsTetheringTest
Bug: 160389275
diff --git a/core/java/android/net/ITetheredInterfaceCallback.aidl b/core/java/android/net/ITetheredInterfaceCallback.aidl
index e3d0759..14aa023 100644
--- a/core/java/android/net/ITetheredInterfaceCallback.aidl
+++ b/core/java/android/net/ITetheredInterfaceCallback.aidl
@@ -17,7 +17,7 @@
 package android.net;
 
 /** @hide */
-interface ITetheredInterfaceCallback {
+oneway interface ITetheredInterfaceCallback {
     void onAvailable(in String iface);
     void onUnavailable();
 }
\ No newline at end of file