Aded hostactive.c and audiostream.c. These are now weak so can be over-ridden by app

module_usb_audio/audiostream/audiostream.c

@@ -0,0 +1,13 @@
+
+/* Deafult implementations of AudioStreamStop() and AudioStreamStart().  Both can be over-ridden */
+void UserAudioStreamStop() __attribute__ ((weak));
+void UserAudioStreamStop()
+{
+    return;
+}  
+
+void UserAudioStreamStart() __attribute__ ((weak));
+void UserAudioStreamStart()
+{
+    return;
+}

module_usb_audio/hostactive/hostactive.c

@@ -0,0 +1,7 @@
+
+void UserHostActive(int active) __attribute__ ((weak));
+void UserHostActive(int active)
+{
+    return;
+}
+