Subnet 4via6 Support

[dcd-projectrose]

Can there be support added for 4via6 Subnets?

[lmagyar]

Hmmm, this could help with colliding/overlapping subnets, especially in case of non-userspace-networking. #201

Sg. like adding an optional config parameter ip4viaip6_site_id and if set then advertise all IPv4 addresses like IPv6 with:

tailscale debug via <ip4viaip6_site_id> <IPv4 subnet>
tailscale up --advertise-routes=fd7a:115c:a1e0:b1a:0:<ip4viaip6_site_id>:<IPv4 subnet IP in hex>/<IPv4 subnet mask + 96>

Note: I'm just another user.