Supplementary Services (de)activation, interrogation added

These patches enhance the Supplementary Service (SS) processing from
only being able to handle USSD to other SS, specifically activation,
deactivation and interrogation of those SS. Registration is not yet
implemented.

include/osmocom/gsm/protocol/gsm_09_02.h has been added with needed
values for SS.

Modified by Harald Welte to keep the old ussd-only functiosn for API/ABI
stability.
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 02c8884..b7c5158 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -44,6 +44,7 @@
 gsm0480_create_unstructuredSS_Notify;
 gsm0480_create_ussd_resp;
 gsm0480_decode_ussd_request;
+gsm0480_decode_ss_request;
 gsm0480_wrap_facility;
 gsm0480_wrap_invoke;