Fetch stage batching of forwarded txs (#6349)

automerge

core/src/fetch_stage.rs

@@ -61,6 +61,10 @@ impl FetchStage {
         while let Ok(more) = recvr.try_recv() {
             len += more.packets.len();
             batch.push(more);
+            // Read at most 1K transactions in a loop
+            if len > 1024 {
+                break;
+            }
         }
 
         if poh_recorder.lock().unwrap().would_be_leader(