Can't get RecvFd/SendFd options
It seems that the RecvFd/SendFd options have been implemented as writeable instead of readable options. From socket.rs:
#[cfg(unix)]
mod unix_impls
{
use super::*;
use crate::options::{RecvFd, SendFd, SetOpt};
impl SetOpt<RecvFd> for Socket {}
impl SetOpt<SendFd> for Socket {}
}