Set media session active when there are calls.

Bug: 15190801
Change-Id: I357778743568cca00fcd8d8dd4b11c21772c3d0e
diff --git a/src/com/android/telecomm/CallsManager.java b/src/com/android/telecomm/CallsManager.java
index 64c1d37..727e44d 100644
--- a/src/com/android/telecomm/CallsManager.java
+++ b/src/com/android/telecomm/CallsManager.java
@@ -118,6 +118,7 @@
         mListeners.add(mCallAudioManager);
         mListeners.add(app.getMissedCallNotifier());
         mListeners.add(mDtmfLocalTonePlayer);
+        mListeners.add(mHeadsetMediaButton);
     }
 
     @Override