l2: change prefetch to prefetchw

L2 prefetches the vlib_buffer_t and then immediately writes to l2 split
horizon group. Changing to the prefetch to a prefetchw.

Type: improvement

Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
Change-Id: If3b7996978ee80f99c55904692c7b3c905f537ce
diff --git a/src/vnet/l2/l2_input_node.c b/src/vnet/l2/l2_input_node.c
index 74625b2..f8dfa36 100644
--- a/src/vnet/l2/l2_input_node.c
+++ b/src/vnet/l2/l2_input_node.c
@@ -252,10 +252,10 @@
 	  /* Prefetch next iteration. */
 	  {
 	    /* Prefetch the buffer header and packet for the N+2 loop iteration */
-	    vlib_prefetch_buffer_header (b[4], LOAD);
-	    vlib_prefetch_buffer_header (b[5], LOAD);
-	    vlib_prefetch_buffer_header (b[6], LOAD);
-	    vlib_prefetch_buffer_header (b[7], LOAD);
+	    clib_prefetch_store (b + 4);
+	    clib_prefetch_store (b + 5);
+	    clib_prefetch_store (b + 6);
+	    clib_prefetch_store (b + 7);
 
 	    clib_prefetch_store (b[4]->data);
 	    clib_prefetch_store (b[5]->data);