ipv4: simplify log message format

This change replaces the existing log format separated by commas and
spaces with space-separated one.

Also removes unnecessary log output in test.

Change-Id: I1bf2b8c463db9174b2ac562533cdd89b72ed39de
Reviewed-on: https://go-review.googlesource.com/16322
Reviewed-by: Ian Lance Taylor <iant@golang.org>
6 files changed