title: Net filter source and destination ports
body: <p>I am currently building stateless firewall module at the linux Kernel, using Netfilter.
  For every packet going in/out i want to extract the layer 4 source and destination ports.I want to extract it regardless of the L4 protocol.
  currently i know how to extract it only based on the l4 protocol: getting the protocol header and getting the port from the header. 
  I want to get it without getting the protocol type, directly from sk_buff struct.
  I would like some help for this topic. tnx!</p>