Don't setsockopt IPV6_V6ONLY under OpenBSD

[dxtr]

The ip6(4) man page states this:

IPV6_V6ONLY int *
[...]. With OpenBSD IPv6 sockets are always IPv6-only, so the socket option is read-only (not modifiable).

This makes ipv6 sockets practically unusable on OpenBSD.

[dxtr]

Actually, why is it even being set at all?

And why is the default 0? That seems like an awful idea