Basic IPv6 Support

[bjoernQ]

This adds the most basic IPv6 support

This is a non-default feature. ("ipv6")

Currently it just creates a link-local address which is used. No DAD is done to detect address conflicts right now. SLAAC / Dhcpv6 is not implemented

Easiest way to test this:

In one of the example folders execute this cargo run --example static_ip --release --features "embedded-svc,wifi,ipv6"

See the link-local address logged at INFO level.

You should be able to ping that address or connect via a browser (with a URL similar to http://[fe80::36b4:72ff:fe4c:4410]:8080/)

The feature also activates Ipv6 support in embassy-net but it seems there is currently no way to set the v6 IP / route there?

Things to be done in future (not part of this PR)

• SLAAC or DhcpV6 support
• Find out how to use IPv6 with embassy-net

[bjoernQ]

Probably SLAAC and DhcpV6 are impossible to implement since smoltcp currently doesn't support multicast for anything but IPv4

However, I was able to not only commission a Matter device but also to control it in Google Home with this ( https://github.com/bjoernQ/matter-rs-experiment/tree/ipv6 )

[MabezDev]

Really nice! Looks good from my perspective!

By the way, what about IPv6 makes the matter demo work?

[bjoernQ]

By the way, what about IPv6 makes the matter demo work?

The problem was that Google Home does the commissioning part fine on v4 but after that it only wants to talk v6. The spec leaves this a bit open so v4 might work with some vendors (and with the official CHIP tool it does) but for some vendors it won't work on v4. The fact that commissioning went through made me believe that everything should also work on v4 so it took me a bit too long to realize that 🤷‍♂️