packetforge: fix order of dst/src address of mac

In the defination of mac node, the order of dst and src address is
reversed. Swap their order in this patch.

Type: fix
Signed-off-by: Ting Xu <ting.xu@intel.com>
Change-Id: I039accc0a881eef12f13c75c5becf8b7df97d525
diff --git a/extras/packetforge/parsegraph/nodes/mac.json b/extras/packetforge/parsegraph/nodes/mac.json
index 6fc4909..fab690b 100644
--- a/extras/packetforge/parsegraph/nodes/mac.json
+++ b/extras/packetforge/parsegraph/nodes/mac.json
@@ -3,13 +3,13 @@
     "name" : "mac",
     "layout" : [
         {
-            "name" : "src",
+            "name" : "dst",
             "size" : "48",
             "format" : "mac",
             "default" : "00:00:00:00:00:01"
         },
         {
-            "name" : "dst",
+            "name" : "src",
             "size" : "48",
             "format" : "mac",
             "default" : "00:00:00:00:00:02"