Communicate audio session ID to downmixer

The audio downmixer effect might need the audio session Id, pass it
 from the track creation in AudioFlinger to the downmix effect
 creation in AudioMixer.

Change-Id: I5e29540542ae89cf4a0cdb537b3e67f04442a20a
diff --git a/services/audioflinger/AudioMixer.h b/services/audioflinger/AudioMixer.h
index 6e34cd1..6333357 100644
--- a/services/audioflinger/AudioMixer.h
+++ b/services/audioflinger/AudioMixer.h
@@ -91,7 +91,7 @@
     // For all APIs with "name": TRACK0 <= name < TRACK0 + MAX_NUM_TRACKS
 
     // Allocate a track name.  Returns new track name if successful, -1 on failure.
-    int         getTrackName(audio_channel_mask_t channelMask);
+    int         getTrackName(audio_channel_mask_t channelMask, int sessionId);
 
     // Free an allocated track by name
     void        deleteTrackName(int name);
@@ -192,7 +192,7 @@
 
         DownmixerBufferProvider* downmixerBufferProvider; // 4 bytes
 
-        int32_t     padding;
+        int32_t     sessionId;
 
         // 16-byte boundary