all: follow convention for generated code comment

Follow the convertion (https://golang.org/s/generatedcode) for generated
code.

Change-Id: I3101fb91db42644ead179ffaeffe0211359ac886
Reviewed-on: https://go-review.googlesource.com/c/net/+/182137
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/ipv6/zsys_netbsd.go b/ipv6/zsys_netbsd.go
index bcada13..e39571e 100644
--- a/ipv6/zsys_netbsd.go
+++ b/ipv6/zsys_netbsd.go
@@ -1,4 +1,4 @@
-// Created by cgo -godefs - DO NOT EDIT
+// Code generated by cmd/cgo -godefs; DO NOT EDIT.
 // cgo -godefs defs_netbsd.go
 
 package ipv6