SI: add missing header

Previous SI10 patch added function without exposing it via public header.
Let's fix this.

Fixes: 600d4eeab71665c0aec0a11a226d231f109534ca
Change-Id: Ia7530e9c8a21f6f99f3aac7baea5cbb38763c4f3
diff --git a/src/gsm/gsm48.c b/src/gsm/gsm48.c
index 6f5c3a3..919500b 100644
--- a/src/gsm/gsm48.c
+++ b/src/gsm/gsm48.c
@@ -438,7 +438,7 @@
 };
 
 /*! return string representation of RR Message Type using the RR short protocol discriminator */
-const char *gsm48_rr_msg_type_short_name(uint8_t msgtype)
+const char *gsm48_rr_short_pd_msg_name(uint8_t msgtype)
 {
 	return get_value_string(rr_msg_type_short_names, msgtype);
 }