Coccinelle: test invalid Packet usage

This coccinelle patches is checking that there is no direct
use of p->pkt or p->pktlen in the code. This variable must be
acceded via GET_PKT_* macros.

qa/coccinelle/access-pkt-packet.cocci

@@ -0,0 +1,55 @@
+@init@
+typedef Packet;
+Packet *p;
+expression E;
+statement S;
+@@
+
+(
+memset(p, ...);
+p->pkt = E;
+|
+p = SCCalloc(...);
+S
+p->pkt = E;
+)
+
+@pktfield depends on !init@
+identifier func !~= "^PacketCopyDataOffset$";
+Packet *p;
+position p1;
+@@
+
+func(...) {
+<...
+p->pkt@p1
+...>
+}
+
+@ script:python @
+p1 << pktfield.p1;
+@@
+
+print "Invalid Packet->pkt usage, GET_PKT_DATA macro must be used at %s:%s" % (p1[0].file, p1[0].line)
+import sys
+sys.exit(1)
+
+@pktlenfield@
+identifier func !~= "^PacketCopyDataOffset$";
+Packet *p;
+position p1;
+@@
+
+func(...) {
+<...
+p->pktlen@p1
+...>
+}
+
+@ script:python @
+p1 << pktlenfield.p1;
+@@
+
+print "Invalid Packet->pktlen usage, GET_PKT_LEN macro must be used at %s:%s" % (p1[0].file, p1[0].line)
+import sys
+sys.exit(1)