Delay pinger on stream bind

Given the serial state machine implemented by lib-gst-meet, it was
expecting an answer to the extdisco:2 iq but got a pong, and wrongly
assumed no STUN/TURN candidates were exposed by the server.

A much better solution would be to match on the iq id as well, but this
will do as a workaround.

lib-gst-meet/src/pinger.rs

@@ -22,6 +22,8 @@ impl Pinger {
     let ping_tx = tx.clone();
     let ping_task = tokio::spawn(async move {
       let mut interval = time::interval(PING_INTERVAL);
+      // The first tick completes immediately.
+      interval.tick().await;
       loop {
         interval.tick().await;
         if let Err(e) = ping_tx.send(Iq::from_get(generate_id(), Ping).into()).await {