Add firewall rules to always allow connection from netns to host

[jamesmcm]

See #59

iptables -A FORWARD -i eth0 -o v-eth1 -j ACCEPT
iptables -A FORWARD -o eth0 -i v-eth1 -j ACCEPT

Need to add both iptables and nftables rules to do the above (and remove them when vopono terminates) - like we do with the masquerade rule on the host.

Interface must be the detected (or provided) interface e.g. ethernet or wireless.

veth tunnel name must be generated name.

[jamesmcm]

In iptables use -I to insert at front (after running other rule insertions), for nftables create specific chain with high priority.

[jamesmcm]

Closed in bf8b7d0