use EINVAL instead of EBADFD (not in POSIX)

[omar-polo]

EBADFD is not defined on OpenBSD (and judging at their errno(2) pages, neither on FreeBSD nor NetBSD.)

There's EBADF but it means 'bad file descriptor', and usually it means that you passed something that wasn't a file descriptor, so I picked EINVAL.

[sjaeckel]

Thanks for highlighting this! We should maybe have CI runs on the BSDs as well.

I just thought whether it wouldn't be better to simply set conn->error to ret resp. err. (In the spirit of all the other "conn interfaces", since they already do that.)

[sjaeckel]

Can I wait a few more days/weeks for a new release, so we can see whether there's other issues popping up?

[omar-polo]

Sure, I can live with a local patch, and it won't prevent the package from being updated on OpenBSD. just fyi: all tests are passing here as usual :)

Thanks!