Missing if_tun constants

[dallenng]

Hello, except for the ioctls, most of the constants from this header are missing. Would you be open to adding bindings for it in this crate or is it out of scope ? I would be willing to work on this with some guidance on the generator if it is wanted.

[sunfishcode]

I'd be open to having bindings for it in this crate. The current scripts for generating ioctl codes are extraordinarily primitive though. I can provide guidance as far as that goes, but at some point, the right answer will be to rewrite the scripts from scratch.

[dallenng]

The Ioctl defines seem to be in the crate already. It is the constants like IFF_TUN, IFF_NO_PI, TUN_F_CSUM, ... that are missing.

[sunfishcode]

Yes, and I think it makes sense to add more, when people need them.

[dallenng]

Thanks, I'll try to make a PR adding this soon.