ipv4: simplify tests and benchmarks

Change-Id: I588bc65b0052efb12b3b7bc2267deedcdad029ce
Reviewed-on: https://go-review.googlesource.com/47371
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matt Layher <mdlayher@gmail.com>
2 files changed