packet buffer headers should have protocol number associated.

Packet headers are now tracked in the packet buffer structure using a special 'header' structure. This structure should maintain what type each header is as well as what layer it is (which is all it has now). In parts of the code where it is important to look at the transport header for example it is expensive to go back to re-examine the IPv6 header to find which kind of transport header is in the transport header storage (tcp? udp? icmp?). Since we already know this information at some stage it is probably worth while to save it with the header.