Fix permissions in demo app.

The ACCESS_NETWORK_STATE permission is only included indirectly which doesn't
work in all build systems.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=197399274

demos/main/src/main/AndroidManifest.xml

@@ -18,6 +18,7 @@
     package="com.google.android.exoplayer2.demo">
 
   <uses-permission android:name="android.permission.INTERNET"/>
+  <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
   <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
   <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>