Support TF-style SAME padding via explicit flag

PiperOrigin-RevId: 276545514
diff --git a/src/xnnpack/operator.h b/src/xnnpack/operator.h
index 62f956a..9b1253a 100644
--- a/src/xnnpack/operator.h
+++ b/src/xnnpack/operator.h
@@ -226,6 +226,7 @@
   void* lookup_table;
   void* pixelwise_buffer;
   struct subconvolution_params* subconvolution_buffer;
+  uint32_t flags;
 
   union {
     union xnn_f32_avgpool_params f32_avgpool_params;