Expose a simple tethering API which includes provision checks.

This CL exposes startTethering and stopTethering functions which also
encapsulate all provisioning check logic. Right now, only silent checks
are implemented, but UI checks will come in a follow-up CL. GTS tests
and Settings changes are under the same topic ID.

BUG: 26247383
Change-Id: I65f61d899594cb3f9035d8496366af17a57a090f
diff --git a/core/java/android/net/IConnectivityManager.aidl b/core/java/android/net/IConnectivityManager.aidl
index 569468e..1a9c9ea 100644
--- a/core/java/android/net/IConnectivityManager.aidl
+++ b/core/java/android/net/IConnectivityManager.aidl
@@ -76,6 +76,10 @@
 
     boolean isTetheringSupported();
 
+    void startTethering(int type, in ResultReceiver receiver, boolean showProvisioningUi);
+
+    void stopTethering(int type);
+
     String[] getTetherableIfaces();
 
     String[] getTetheredIfaces();