Introduce Wireguard support to bird

[Toke Høiland-Jørgensen]

Janne Heß <janne at hess.ooo> writes:

> Hey everyone,
>
> as advertised, I have completed the Wireguard support.
> You might see that I am not really a C expert, but I hope the code is good enough.
> If you need me to change anything or have additional questions, just
> let me know.

Hi Janne

Awesome that you have taken the time to implement this!

I'll let the Bird maintainers comment on the approach of embedding the
wireguard netlink library; but I have two other concerns:

- As far as I can tell there's nothing preventing Bird from removing
  AllowedIPs that it did not itself install from an interface, right?

- The algorithm is basically O(P*M*N) for inserting N routes on an
  interface with P peers that each have M existing AllowedIPs. That is
  not going to scale very far :/

-Toke