Fix issue 5381089: problem with A2DP music volume

This problem only occurs when audio effects are present and
the music volume is applied by one effect engine.
When connecting or disconnecting A2DP, audio effects are moved from
one mixer thread to another. When removed from the source thread,
the effect is stopped but it is not restarted when added to the
destination thread.
This regression was introduced by commit 21b5c47e.

Change-Id: I4cc578d8d760ec65b185032b6fda98c739d331bc
diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index 2e05593..ed9d81e 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -1117,6 +1117,7 @@
         status_t         setDevice(uint32_t device);
         status_t         setVolume(uint32_t *left, uint32_t *right, bool controller);
         status_t         setMode(uint32_t mode);
+        status_t         start();
         status_t         stop();
         void             setSuspended(bool suspended);
         bool             suspended();