gsm: Introduce API osmo_gsm48_rest_octets_si13_decode

Related: SYS#5358
Change-Id: I74fb0a3afc1ac4aadbfc609b882d929401f790eb
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index efa23e6..0ea0678 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -320,6 +320,7 @@
 osmo_gsm48_rest_octets_si6_encode;
 osmo_gsm48_rest_octets_si3_encode;
 osmo_gsm48_rest_octets_si4_encode;
+osmo_gsm48_rest_octets_si13_decode;
 osmo_gsm48_rest_octets_si13_encode;
 osmo_gsm48_rest_octets_si3_decode;
 osmo_gsm48_rest_octets_si4_decode;