fix(relay): close stream once done sending

Not explicitly closing a stream can lead to stream resets in the happy path once the stream is dropped. Instead, explicitly close the stream once the local node is done sending data.

Related: #4747.

Pull-Request: #4776.

protocols/relay/src/protocol/outbound_hop.rs

@@ -124,6 +124,8 @@ pub(crate) async fn make_reservation(stream: Stream) -> Result<Reservation, Rese
 
     substream.send(msg).await?;
 
+    substream.close().await?;
+
     let proto::HopMessage {
         type_pb,
         peer: _,