Update Settings UI regarding tethering.

If tethering is disabled (build var or a gservices property) for the device,
don't show any of the tethering options.  If Usb Tethering is disabled (config.xml) don't show
Usb Options.  If Wifi Tethering is disabled (config.xml) don't show Wifi Options.
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 67f0cde..ad4596e 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -171,8 +171,7 @@
         </activity>
 
         <activity android:name=".TetherSettings"
-                android:configChanges="orientation|keyboardHidden"
-                android:launchMode="singleTask">
+                android:clearTaskOnLaunch="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.DEFAULT" />