add osmo_prim_operation_name()

Also remove the explicit array dimension from the .h file.

Change-Id: I9f43428af654a5674ac3035fe4db1394aac7a7af
diff --git a/include/osmocom/core/prim.h b/include/osmocom/core/prim.h
index 99eabff..8e6b436 100644
--- a/include/osmocom/core/prim.h
+++ b/include/osmocom/core/prim.h
@@ -30,7 +30,11 @@
 	PRIM_OP_CONFIRM,	/*!< confirm */
 };
 
-extern const struct value_string osmo_prim_op_names[5];
+extern const struct value_string osmo_prim_op_names[];
+static inline const char *osmo_prim_operation_name(enum osmo_prim_operation val)
+{
+	return get_value_string(osmo_prim_op_names, val);
+}
 
 /*!< The upper 8 byte of the technology, the lower 24 bits for the SAP */
 #define _SAP_GSM_SHIFT	24