Use AUDIO_SESSION_ALLOCATE instead of 0

Also fix a couple of places where we were using AUDIO_SESSION_OUTPUT_MIX,
which happens to also be equal to 0, but has a different meaning.

Change-Id: I90e39be3b89f5021a96d9e3b8d10929013ca977f
diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index e163f88..2717549 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -185,7 +185,7 @@
                                     callback_t cbf       = NULL,
                                     void* user           = NULL,
                                     int notificationFrames = 0,
-                                    int sessionId        = 0,
+                                    int sessionId        = AUDIO_SESSION_ALLOCATE,
                                     transfer_type transferType = TRANSFER_DEFAULT,
                                     const audio_offload_info_t *offloadInfo = NULL,
                                     int uid = -1);
@@ -210,7 +210,7 @@
                                     callback_t cbf      = NULL,
                                     void* user          = NULL,
                                     int notificationFrames = 0,
-                                    int sessionId       = 0,
+                                    int sessionId       = AUDIO_SESSION_ALLOCATE,
                                     transfer_type transferType = TRANSFER_DEFAULT,
                                     const audio_offload_info_t *offloadInfo = NULL,
                                     int uid = -1);
@@ -248,7 +248,7 @@
                             int notificationFrames = 0,
                             const sp<IMemory>& sharedBuffer = 0,
                             bool threadCanCallJava = false,
-                            int sessionId       = 0,
+                            int sessionId       = AUDIO_SESSION_ALLOCATE,
                             transfer_type transferType = TRANSFER_DEFAULT,
                             const audio_offload_info_t *offloadInfo = NULL,
                             int uid = -1);