IPV6_PKTINFO missing in Darwin

[mcginty]

This seems to be because it's undefined unless one of either __APPLE_USE_RFC_2292 or __APPLE_USE_RFC_3542 is also defined (explained in the XNU source here).

It appears to be a bit of a hairy compatibility situation, but the RFC 3542 code was added 5 years ago, so it's not exactly brand new any more. Is there any precedent for these kinds of situations in libc? It would be nice to have these constants and the in6_pktinfo struct available in some form or another.

[gnzlbg]

PRs welcome.

[pusateri]

I think this was fixed in #980 and can be closed.

[gnzlbg]

Thanks!