fixup! Re-design the StreamMuxer trait

Favor local work over remote work.

muxers/mplex/src/lib.rs

@@ -97,12 +97,6 @@ where
         &mut self,
         cx: &mut Context<'_>,
     ) -> Poll<io::Result<StreamMuxerEvent<Self::Substream>>> {
-        if let Poll::Ready(mplex_id) = self.io.lock().poll_next_stream(cx)? {
-            let substream = Substream::new(mplex_id, self.io.clone());
-
-            return Poll::Ready(Ok(StreamMuxerEvent::InboundSubstream(substream)));
-        }
-
         if let Poll::Ready((mplex_id, outbound_id)) = self
             .outbound_substreams
             .poll(|| Pin::new(&mut self.io.lock()).poll_open_stream(cx))?
@@ -115,6 +109,12 @@ where
             )));
         }
 
+        if let Poll::Ready(mplex_id) = self.io.lock().poll_next_stream(cx)? {
+            let substream = Substream::new(mplex_id, self.io.clone());
+
+            return Poll::Ready(Ok(StreamMuxerEvent::InboundSubstream(substream)));
+        }
+
         Poll::Pending
     }