Recent merge of cert-v2 support introduced the ability to tunnel IPv6. However, FreeBSD's IPv6 tunneling does not work for 2 reasons:
* The ifconfig commands did not work for IPv6 addresses
* The tunnel device was not configured for link-layer mode, so it only supported IPv4
This PR improves FreeBSD tunneling support in 3 ways:
* Use ioctl instead of exec'ing ifconfig to configure the interface, with additional logic to support IPv6
* Configure the tunnel in link-layer mode, allowing IPv6 traffic
* Use readv() and writev() to communicate with the tunnel device, to avoid the need to copy the packet buffer
* upgrade to yaml.v3
The main nice fix here is that maps unmarshal into `map[string]any`
instead of `map[any]any`, so it cleans things up a bit.
* add config.AsBool
Since yaml.v3 doesn't automatically convert yes to bool now, for
backwards compat
* use type aliases for m
* more cleanup
* more cleanup
* more cleanup
* go mod cleanup
With the previous implementation, we check if route.MTU is greater than zero,
but it will always be because we set it to the default MTU in
parseUnsafeRoutes. This change leaves it as zero in parseUnsafeRoutes so
it can be examined later.
