Add qemu-dm-sipb written by andersk to get us the domain ID in qemu-ifup
Add vif-sipbroute, a version of vif-route that does better netwwork
isolation and has initial but useless ipv6 support. This version also
uses arpspoof to take over an address for domain migrations.
Add init script to enable rp_filter, proxy_arp and forwarding for the network config.