libnetlink: add size argument to rtnl_talk

There have been several instances where response from kernel
has overrun the stack buffer from the caller. Avoid future problems
by passing a size argument.

Also drop the unused peer and group arguments to rtnl_talk.
diff --git a/tc/tc_class.c b/tc/tc_class.c
index 877048a..3acd030 100644
--- a/tc/tc_class.c
+++ b/tc/tc_class.c
@@ -153,7 +153,7 @@
 		}
 	}
 
-	if (rtnl_talk(&rth, &req.n, 0, 0, NULL) < 0)
+	if (rtnl_talk(&rth, &req.n, NULL, 0) < 0)
 		return 2;
 
 	return 0;