src: NAT support for intervals in maps

src: NAT support for intervals in maps

This patch allows you to specify an interval of IP address in maps.

 table ip x {
        chain y {
                type nat hook postrouting priority srcnat; policy accept;
                snat ip interval to ip saddr map { 10.141.11.4 : 192.168.2.2-192.168.2.4 }
        }
 }

The example above performs SNAT to packets that comes from 10.141.11.4
to an interval of IP addresses from 192.168.2.2 to 192.168.2.4 (both
included).

You can also combine this with dynamic maps:

 table ip x {
        map y {
                type ipv4_addr : interval ipv4_addr
                flags interval
                elements = { 10.141.10.0/24 : 192.168.2.2-192.168.2.4 }
        }

        chain y {
                type nat hook postrouting priority srcnat; policy accept;
                snat ip interval to ip saddr map @y
        }
 }

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>