04.80: New gsm0480_gen_{reject,return_error}() functions

Add functions to generate TS 04.80 (supplementary services)
Reject and ReturnError components.

Change-Id: I6e5ee39c3d03364f7833ec717593d5ddb0a4c5f9
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index d21514c..b44cfd2 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -99,6 +99,8 @@
 gsm0480_op_code_names;
 gsm0480_msgb_alloc_name;
 gsm0480_gen_ussd_resp_7bit;
+gsm0480_gen_return_error;
+gsm0480_gen_reject;
 
 gsm0502_calc_paging_group;