fix

Author: sushanb

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/internal/csm/tracers/BuiltinMetricsTracer.java

@@ -400,7 +400,8 @@ private void recordAttemptCompletion(@Nullable Throwable throwable) {
           code,
           Comparators.max(remainingDeadlineAtAttemptStart, Duration.ZERO));
     }
-
+    // if we don't have t4t7 latency from gfe, we use dur between initial metadata sent and initial
+    // metadata recv
     if (sidebandData.getGfeTiming() != null) {
       recorder.serverLatency.record(
           clientInfo,