Started to parse the actual packets for more friendlier callbacks

So far only support for udp with ipv4, not fully tested it just yet
but it should work..

Signed-off-by: Toon Schoenmakers <nighteyes1993@gmail.com>
Added a working IPv4 UDP example

And fixed a couple of internal bugs which would stop this callback
from working..

Signed-off-by: Toon Schoenmakers <nighteyes1993@gmail.com>
Apparently we need to include stdio.h for NULL with gcc

I did not know that clang handles this without issues, neat.

Signed-off-by: Toon Schoenmakers <nighteyes1993@gmail.com>