Add USDD code from Mike Haben
This is the initial checkin of the USSD code from Mike Haben. I didn't
put it in the main branch as I think it still needs some cleanup.
diff --git a/openbsc/include/openbsc/ussd.h b/openbsc/include/openbsc/ussd.h
new file mode 100644
index 0000000..e7bd6d6
--- /dev/null
+++ b/openbsc/include/openbsc/ussd.h
@@ -0,0 +1,10 @@
+#ifndef _USSD_H
+#define _USSD_H
+
+/* Handler function for mobile-originated USSD messages */
+
+#include <openbsc/msgb.h>
+
+int handle_rcv_ussd(struct msgb *msg);
+
+#endif