xds: apply initial backoff even if we got a response on the previous call (#29251)

src/core/ext/xds/xds_client.cc

@@ -683,18 +683,12 @@ void XdsClient::ChannelState::RetryableCall<T>::Orphan() {
 
 template <typename T>
 void XdsClient::ChannelState::RetryableCall<T>::OnCallFinishedLocked() {
-  const bool seen_response = calld_->seen_response();
+  // If we saw a response on the current stream, reset backoff.
+  if (calld_->seen_response()) backoff_.Reset();
   calld_.reset();
-  if (seen_response) {
-    // If we lost connection to the xds server, reset backoff and restart the
-    // call immediately.
-    backoff_.Reset();
-    StartNewCallLocked();
-  } else {
-    // If we failed to connect to the xds server, retry later.
+  // Start retry timer.
   StartRetryTimerLocked();
 }
-}
 
 template <typename T>
 void XdsClient::ChannelState::RetryableCall<T>::StartNewCallLocked() {