fix: reset stream metrics batch on flush

Author: amokfa

uplink/src/base/bridge/stream.rs

@@ -109,6 +109,7 @@ impl Stream {
     /// Triggers flush and async channel send if not empty
     pub async fn flush(&mut self) -> Result<(), Error> {
         if !self.is_empty() {
+            self.metrics.add_batch();
             let buf = self.take_buffer();
             self.tx.send_async(Box::new(buf)).await?;
         }