Add permission protections in sample apps

Protect the download receiver with ACT_AS_EMBMS_MIDDLEWARE and declare
its usage in the sample middleware.

Change-Id: Ic7e6ac247dab18a6be3754f211055417c83c243d
diff --git a/testapps/EmbmsTestDownloadApp/AndroidManifest.xml b/testapps/EmbmsTestDownloadApp/AndroidManifest.xml
index b81b928..e93cd19 100644
--- a/testapps/EmbmsTestDownloadApp/AndroidManifest.xml
+++ b/testapps/EmbmsTestDownloadApp/AndroidManifest.xml
@@ -28,9 +28,9 @@
         </activity>
 
         <!-- This is the receiver defined by the MBMS api. -->
-        <!-- TODO: protect this with a permission -->
         <receiver
             android:name="android.telephony.mbms.MbmsDownloadReceiver"
+            android:permission="android.permission.SEND_EMBMS_INTENTS"
             android:enabled="true"
             android:exported="true">
         </receiver>