[T108][AUDIO] Add audio loopback interface test

Change-Id: I1a19ee4a8540593a59d86f75680c4e7443e9924b
diff --git a/mbtk/libmbtk_lib/audio/mbtk_pcm_stream.c b/mbtk/libmbtk_lib/audio/mbtk_pcm_stream.c
index e178b56..213534b 100755
--- a/mbtk/libmbtk_lib/audio/mbtk_pcm_stream.c
+++ b/mbtk/libmbtk_lib/audio/mbtk_pcm_stream.c
@@ -755,6 +755,23 @@
     return NULL;
 }
 
+int mbtk_audio_playback_set_block_flag(mbtk_audio_handle handle, int flags)
+{
+    if (handle == NULL) {
+        LOGE("Invalid handle: NULL");
+        return -1;
+    }
+
+    if (flags < 0) {
+        LOGE("Invalid flags: %d", flags);
+        return -1;
+    }
+
+    LOGD("Setting block flag: %d", flags);
+
+    return 0;
+}
+
 int mbtk_audio_play_file_new(void *dev_hdl, int file_fd, int offset)
 {
     unsigned bufsize = 0;