Convert to use rta_getattr_ functions

User new functions (inspired by libmnl) to do type safe access
of routeing attributes
diff --git a/tc/tc_class.c b/tc/tc_class.c
index 3a1a0ac..de18fd1 100644
--- a/tc/tc_class.c
+++ b/tc/tc_class.c
@@ -191,7 +191,7 @@
 		else
 			print_tc_classid(abuf, sizeof(abuf), t->tcm_handle);
 	}
-	fprintf(fp, "class %s %s ", (char*)RTA_DATA(tb[TCA_KIND]), abuf);
+	fprintf(fp, "class %s %s ", rta_getattr_str(tb[TCA_KIND]), abuf);
 
 	if (filter_ifindex == 0)
 		fprintf(fp, "dev %s ", ll_index_to_name(t->tcm_ifindex));