async_fd fails to deregister the fd on into_inner

[bdonlan]

Version
Current master

Platform

Linux [redacted] 5.4.[redacted #1 SMP Thu Oct 8 22:11:29 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

Description

The following code fails because AsyncFd does not deregister the inner fd:

#[tokio::test]
async fn reregister() {
    let (a, _b) = socketpair();

    let afd_a = AsyncFd::new(a).unwrap();
    let a = afd_a.into_inner();
    AsyncFd::new(a).unwrap();
}