factor out gen of USSD notify and release complete to libosmocore

Both libmsc and libbsc will need distinct gsm0480_send_ussdNotify() and
gsm0480_send_releaseComplete() functions, since there will be distinct
subscriber connection structs.

Rename to msc_send_ussd_notify() and msc_send_ussd_release_complete(), and add
the same in libbsc with bsc_ prefix in new file gsm_04_80_utils.c.

In preparation of this patch, the message generation part of these functions
has been added to libosmocore as gsm0480_create_ussd_notify() and
gsm0480_create_ussd_release_complete(). Use these.

Adjust all libmsc and libbsc callers according to use the msc_* or bsc_*
implementation, respectively.

Change-Id: I33a84e3c28576ced91d2ea24103123431f551173
diff --git a/openbsc/include/openbsc/gsm_04_80.h b/openbsc/include/openbsc/gsm_04_80.h
index 74701ac..d65f640 100644
--- a/openbsc/include/openbsc/gsm_04_80.h
+++ b/openbsc/include/openbsc/gsm_04_80.h
@@ -14,7 +14,12 @@
 			     const struct msgb *msg, 
 			     const struct ss_request *request);
 
-int gsm0480_send_ussdNotify(struct gsm_subscriber_connection *conn, int level, const char *text);
-int gsm0480_send_releaseComplete(struct gsm_subscriber_connection *conn);
+int msc_send_ussd_notify(struct gsm_subscriber_connection *conn, int level,
+			 const char *text);
+int msc_send_ussd_release_complete(struct gsm_subscriber_connection *conn);
+
+int bsc_send_ussd_notify(struct gsm_subscriber_connection *conn, int level,
+			 const char *text);
+int bsc_send_ussd_release_complete(struct gsm_subscriber_connection *conn);
 
 #endif