Use cool down period if TCP accept fails

[mvd-ows]

As above.

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This change is 

[faern]

Reviewed 2 of 3 files at r1.
Reviewable status: 2 of 3 files reviewed, 2 unresolved discussions (waiting on @mvd-ows)

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.github/workflows/ci.yml line 68 at r1 (raw file):

        include:
#          - os: ubuntu-latest
#            rust: nightly

This has to be reverted before merged.

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src/tcp2udp.rs line 13 at r1 (raw file):

use std::time::Duration;
use tokio::net::{TcpListener, TcpSocket, TcpStream, UdpSocket};
use tokio::time::{sleep, Duration as tokio_Duration};

Tokio just re-exports std::time::Duration. So you don't need to import it here, the regular Duration is already in scope.