gprs_ns2: Introduce gprs_ns2_lltype_str() for link layer name

Change-Id: I4b257c09d9d3c97d6da04240c7a74a95c7c93675
diff --git a/include/osmocom/gprs/gprs_ns2.h b/include/osmocom/gprs/gprs_ns2.h
index 99764d0..4575329 100644
--- a/include/osmocom/gprs/gprs_ns2.h
+++ b/include/osmocom/gprs/gprs_ns2.h
@@ -47,11 +47,16 @@
 };
 
 extern const struct value_string gprs_ns2_prim_strs[];
+extern const struct value_string gprs_ns2_lltype_strs[];
 
 /*! Obtain a human-readable string for NS primitives */
 static inline const char *gprs_ns2_prim_str(enum gprs_ns2_prim val)
 { return get_value_string(gprs_ns2_prim_strs, val); }
 
+/*! Obtain a human-readable string for NS link-layer type */
+static inline const char *gprs_ns2_lltype_str(enum gprs_ns2_ll val)
+{ return get_value_string(gprs_ns2_lltype_strs, val); }
+
 /*! Osmocom NS primitives according to 48.016 5.2.2.4 Service primitves */
 enum gprs_ns2_congestion_cause {
 	NS_CONG_CAUSE_BACKWARD_BEGIN,