create ipinfo print_known_subnets

Signed-off-by: Etienne Basset <etienne.basset@ensta.org>
correct ipinfo ouput formatting

Signed-off-by: Etienne Basset <etienne.basset@ensta.org>
add a [all|ipv4|ipv6] switch to ipinfo commands, to print all recognized subnets

Signed-off-by: Etienne Basset <etienne.basset@ensta.org>