bridge_driver: handle DNS over IPv6
bridge_driver: handle DNS over IPv6

* dnsmasq listens on all defined IPv[46] addresses for network
* Add ip6tables rules to allow DNS traffic to host
(cherry picked from commit 47969c055ed211f5436cd5a879afb88676f59b3f)

Signed-off-by: Steve Hodgson <eb20a6615749cf04ff61aa37e18f749ed6d01446@solarflare.com>

sshah-solarflare/Libvirt-PCI-passthrough-,sshah-solarflare/Libvirt-PCI-passthrough-,sshah-solarflare/Libvirt-PCI-passthrough-,sshah-solarflare/Libvirt-PCI-passthrough-,sshah-solarflare/Libvirt-PCI-passthrough-