Function settle 

async fn settle<R: Radio>(
    stack: &mut NodeStack<'_, R>,
    ticket: &SendProgressTicket,
    args: &SendArgs,
    before: MacCounters,
) -> Result<()>
where
    R::Error: Debug,

Pump the radio until the message is done, or until patience runs out.

“Done” means two different things. An acknowledged send is done when the MAC says so — an ack arrived, or every retransmission timed out. A send that asked for no acknowledgment has no receipt to track, so its ticket is finished the moment it is issued, before the frame has been anywhere near the radio; what finishes that one is the frame actually going out, which the MAC’s own transmit counters report.