rest_octets: Add function to parse SI3 rest octets

Change-Id: I690cf308311f910005a325d50f5d5d825678d2b2
Related: OS#3075
Related: OS#4023
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 56fed0f..84d71e6 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -309,6 +309,7 @@
 osmo_gsm48_rest_octets_si3_encode;
 osmo_gsm48_rest_octets_si4_encode;
 osmo_gsm48_rest_octets_si13_encode;
+osmo_gsm48_rest_octets_si3_decode;
 gsm48_rr_msg_name;
 gsm48_cc_state_name;
 gsm48_construct_ra;