Support ipv{n}.address=none for ovn networks

[tomponline]

Support ipv{n}.address=none for ovn networks to allow completely isolated networks.

This would:

• Disable auto IP (DHCP/RA) for the relevant IP protocol(s).
• Disable DNS forwarding for the relevant IP protocol(s)
• Remove the relevant IP(s) from the router's external switch interface.
• Remove the relevant IP(s) from the router's internal switch interface.
• Disable router uplink connection entirely (if both IPv4 and IPv6 were disabled) (allow for no uplink network).

[bryanyork]

Yes, would love the ability to create switches between containers that can be used to chain interfaces together for QoS/SQM, etc.
By default I get lxc network create ovn-virtual-network --type=ovn network=dummy ipv4.nat=false ipv6.nat=false ipv4.address=none ipv6.address=none Error: No internal IPs defined for network router

[tomponline]

semi-related to lxc/incus#1189

[tomponline]

see also lxc/incus#1070