Fix issue 2192181: AudioFlinger must provide separated methods to set VOICE_CALL stream volume and down link audio volume.

Added setVoiceVolume() method to AudioSystem, AudioFlinger, IAudioFlinger, AudioPolicyService.
Removed call to AudioHardwareInterface::setVoiceVolume() from AudioFlinger::setStreamVolume().
diff --git a/include/media/AudioSystem.h b/include/media/AudioSystem.h
index 57f8102..a7c8a0a 100644
--- a/include/media/AudioSystem.h
+++ b/include/media/AudioSystem.h
@@ -220,6 +220,7 @@
     static status_t getInputBufferSize(uint32_t sampleRate, int format, int channelCount,
         size_t* buffSize);
 
+    static status_t setVoiceVolume(float volume);
 
     //
     // AudioPolicyService interface
diff --git a/include/media/IAudioFlinger.h b/include/media/IAudioFlinger.h
index 8018568..a46c727 100644
--- a/include/media/IAudioFlinger.h
+++ b/include/media/IAudioFlinger.h
@@ -102,10 +102,10 @@
 
     virtual     status_t    setParameters(int ioHandle, const String8& keyValuePairs) = 0;
     virtual     String8     getParameters(int ioHandle, const String8& keys) = 0;
-    
+
     // register a current process for audio output change notifications
     virtual void registerClient(const sp<IAudioFlingerClient>& client) = 0;
-    
+
     // retrieve the audio recording buffer size
     virtual size_t getInputBufferSize(uint32_t sampleRate, int format, int channelCount) = 0;
 
@@ -128,6 +128,8 @@
     virtual status_t closeInput(int input) = 0;
 
     virtual status_t setStreamOutput(uint32_t stream, int output) = 0;
+
+    virtual status_t setVoiceVolume(float volume) = 0;
 };