command would add incorrect routing entries if network numbers weren't
fully "spelled" out according to their class. For example:
# route add 128.0/16 (works)
# route add 128/16 (doesn't work)
# route add 193.0.0/24 (works)
# route add 193/24 (doesn't work)
Also, rework the way a netmask is deduced from network number if
it [netmask] is not specified.
Submitted by: Nuno Antunes <nuno.antunes@gmail.com> (mostly)
MFC after: 1 week