gsm_utils: add enum osmo_rat_type, from osmo-msc enum ran_type

In the MSC, we have RAN types GERAN_A and UTRAN_IU, now we need a similar enum
in osmo-hlr's GSUP client.

Naming: in the MAP specifications, the RAN type is mostly called RAT type,
(Radio Access Network vs. Radio Access Technology?). Since GSUP is more about
MAP messages, I'm calling the enum osmo_rat_type.

Rationale: osmo-msc and osmo-sgsn want to tell the osmo-hlr which RAT a
subscriber is calling on. A subsequent patch will extend the GSUP protocol and
add a RAT types IE.

Change-Id: I659687aef7a4d67ca372a39fef31dee07aed7631
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 76b3fd0..bb97878 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -553,5 +553,7 @@
 sgsap_ue_emm_mode_names;
 sgsap_ie_tlvdef;
 
+osmo_rat_type_names;
+
 local: *;
 };