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/src/Makefile.am b/openbsc/src/Makefile.am
index 919e075..2f715bb 100644
--- a/openbsc/src/Makefile.am
+++ b/openbsc/src/Makefile.am
@@ -14,7 +14,7 @@
libmsc_a_SOURCES = gsm_subscriber.c db.c telnet_interface.c \
mncc.c rtp_proxy.c gsm_04_08.c gsm_04_11.c transaction.c \
- token_auth.c rrlp.c
+ token_auth.c rrlp.c gsm_04_80.c ussd.c
libvty_a_SOURCES = vty/buffer.c vty/command.c vty/vector.c vty/vty.c