Currently it seems to be more work to fix the ip validation in
ubox project (validate/validate.c). Therefore we just validate it
as string.

Fixes #9

Signed-off-by: Tim Niemeyer <tim@tn-x.org>
Reviewed-by: Jan Kraus <mayosemmel@gmail.com>
Reviewed-by: Tobias Klaus <tk+ff@meskal.net>