convert openbsc to use libosmocore-0.1.1 API

the 0.1.1 API is cleaned up and removes all exported global static
arrays (like rlm_cause_strs).  There are now proper accessor functions.
diff --git a/openbsc/src/abis_rsl.c b/openbsc/src/abis_rsl.c
index 60e64cf..e7844af 100644
--- a/openbsc/src/abis_rsl.c
+++ b/openbsc/src/abis_rsl.c
@@ -1234,7 +1234,7 @@
 
 	LOGP(DRLL, LOGL_ERROR, "%s ERROR INDICATION cause=%s\n",
 		gsm_lchan_name(msg->lchan),
-		get_value_string(rsl_rlm_cause_strs, rlm_cause[1]));
+		rsl_rlm_cause_name(rlm_cause[1]));
 
 	rll_indication(msg->lchan, rllh->link_id, BSC_RLLR_IND_ERR_IND);