[libvirt] [PATCH 00/13] IPv6 support for virtual networks using bridge driver

Finally! Most of this patchset is setup for patch 09/13, which updates the network XML parser to support IPv6, and 12/13, which turns on IPv6 in the bridge driver. In order to have each patch individually pass make check and (otherwise function properly in case someone is doing a bisect), there is a bit of extra code churn (lines that are changed in one patch, only to be changed again in a later patch); I tried to minimize this as much as possible. For for IPv6 to work correctly, target *and build* systems will now need to have ip6tables and radvd available. The way I added ip6tables into autoconfigure.ac is identical to existing iptables, and the way I added radvd is identical to dnsmasq. Unfortunately this doesn't communicate the requirement downstream in a programmatic fashion, so I guess we need to make sure that this is adequately reported in the next set of release notes. There is a remaining problem, outlined in PATCH 13/13, which I would like some input on - there is a race between radvd writing its pidfile and libvirtd reading it, and a couple possible ways to fix it, neither of which is optimal. If anyone has a different idea, I'd like to hear it (I'm leaning towards option 2 right now - it creates an extra file, but behavior is 100% correct).