short-circuit retry code when retries not configured (#26840)

src/core/ext/filters/client_channel/retry_filter.cc

@@ -2189,6 +2189,11 @@ void RetryFilter::CallData::StartTransportStreamOpBatch(
   }
   // If we do not yet have a call attempt, create one.
   if (call_attempt_ == nullptr) {
+    // If there is no retry policy, then commit retries immediately.
+    // This ensures that the code below will always jump to the fast path.
+    // TODO(roth): Remove this special case when we implement
+    // transparent retries.
+    if (retry_policy_ == nullptr) retry_committed_ = true;
     // If this is the first batch and retries are already committed
     // (e.g., if this batch put the call above the buffer size limit), then
     // immediately create an LB call and delegate the batch to it.  This