ipv4: use of internal/netreflect package

Change-Id: Idffb7eace4d7913e7dfad2715d10dcd1762f83e4
Reviewed-on: https://go-review.googlesource.com/27733
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
22 files changed