gsm_utils: Add osmo_dump_gsmtime

Used by osmo-bts, moved from osmo-bts l1sap.c:dump_gsmtime.

Change-Id: Ib5452e2c20f53006c0f6d197fb055728947125d8
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index e992a4f..ad7e013 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -274,6 +274,7 @@
 gsm_fn2gsmtime;
 gsm_get_octet_len;
 gsm_gsmtime2fn;
+osmo_dump_gsmtime;
 
 gsm_milenage;
 gsm_septet_encode;