If IPv6 is configured in the VM, and it is providing network to others,
apply IPv6 firewall similar to the IPv4 one (including NAT for outgoing
traffix), instead of blocking everything. Also, enable IP forwarding for
IPv6 in such a case.
FixesQubesOS/qubes-issues#718
There were multiple problems with reusing existing one:
- need to sync with upstream changes (configuration path etc)
- conflicts resolution on updates
- lack of iptables --wait, which causes firewall fail to load sometimes
QubesOS/qubes-issues#1067