action handling: add test to avoid direct access

Direct access to the action field of Packet structure is not
allowed.

qa/coccinelle/action-pkt.cocci

@@ -0,0 +1,15 @@
+@action@
+typedef Packet;
+Packet *p;
+position p1;
+@@
+
+p->action@p1
+
+@ script:python @
+p1 << action.p1;
+@@
+
+print "Invalid usage of p->action, please use macro at %s:%s" % (p1[0].file, p1[0].line)
+import sys
+sys.exit(1)