`close` can fail on FreeBSD with `ECONNRESET`

[talex5]

On FreeBSD, closing a socket can return ECONNRESET. See https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=159179 and python/cpython#2565.

Eio should ignore this error automatically. This is how Python handles it:

https://github.com/python/cpython/blob/15d6506d175780bb29e5fcde654e3860408aa93e/Modules/socketmodule.c#L6215-L6218

https://man.freebsd.org/cgi/man.cgi?query=close&sektion=2 says:

In case of any error except EBADF, the supplied file descriptor is deallocated and therefore is no longer valid.