Fix virtual network problems on lizard

When using this kernel, the firewalling configuration seems messy for the less, resulting in quite random virtual network problems. We face bugs in the DNAT where VMs supposed to be reachable from the outside ain’t anymore, or situations where the VMs can’t get a DHCP lease.

There is probably some conflicts between our shorewall iptables rules and libvirt’s ones, but that’s surprising to hit this bug only on this kernel.

Parent Task: #7631 (closed)

Original created by @bertagaz on 8506 (Redmine)