fixes

src/core/ext/census/grpc_filter.c

@@ -78,7 +78,8 @@ static void client_mutate_op(grpc_call_element *elem,
   call_data *calld = elem->call_data;
   channel_data *chand = elem->channel_data;
   if (op->send_initial_metadata) {
-    extract_and_annotate_method_tag(op->send_initial_metadata, calld, chand);
+    extract_and_annotate_method_tag(
+        op->payload->send_initial_metadata.send_initial_metadata, calld, chand);
   }
 }
 
@@ -107,9 +108,12 @@ static void server_mutate_op(grpc_call_element *elem,
   call_data *calld = elem->call_data;
   if (op->recv_initial_metadata) {
     /* substitute our callback for the op callback */
-    calld->recv_initial_metadata = op->recv_initial_metadata;
-    calld->on_done_recv = op->recv_initial_metadata_ready;
-    op->recv_initial_metadata_ready = &calld->finish_recv;
+    calld->recv_initial_metadata =
+        op->payload->recv_initial_metadata.recv_initial_metadata;
+    calld->on_done_recv =
+        op->payload->recv_initial_metadata.recv_initial_metadata_ready;
+    op->payload->recv_initial_metadata.recv_initial_metadata_ready =
+        &calld->finish_recv;
   }
 }