Override tethering module APK-in-APEX for Go variant

Bug: 155604224
Test: build
Change-Id: I4147173b5f3668491ff9cb7f1f86715b036d6d4b
diff --git a/Tethering/Android.bp b/Tethering/Android.bp
index bfb6524..83f761f 100644
--- a/Tethering/Android.bp
+++ b/Tethering/Android.bp
@@ -109,6 +109,7 @@
     manifest: "AndroidManifest_InProcess.xml",
     // InProcessTethering is a replacement for Tethering
     overrides: ["Tethering"],
+    apex_available: ["com.android.tethering"],
 }
 
 // Updatable tethering packaged as an application