add osmo_mi_name(), for MI-to-string like "IMSI-123456"

We have gsm48_mi_to_string() and osmo_bcd2str(), but still lack a function that
conveniently prints both MI type and value in one function call.

Related: http://people.osmocom.org/neels/mi_mi_mi.jpg
Change-Id: I7798c3ef983c2e333b2b9cbffef6f366f370bd81
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index bb97878..8b7a164 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -325,6 +325,7 @@
 gsm48_set_dtx;
 gsm48_dtx_mode;
 gsm48_mi_type_name;
+osmo_mi_name;
 gsm48_mcc_mnc_to_bcd;
 gsm48_mcc_mnc_from_bcd;
 gsm48_generate_lai2;