Adapting the packet module into the new requirements.

This is bound to be unstable.
Adapting packet, core and fragment database to the new requirements.
Still under construction.
Today's scarce tweaks. It's all comments and new validations.
Applying new requirements to ttp and improving the other ones.
That's the last module that needed tweaking.
From now on I'll just address unit tests and bugs.
Some unit tests.
Because the different kernels sum four different ways to manage fragments, this is not scaling well. I'm going to move most of the fragmentation testing to a new framework.
Review. Bug fixing and TODO addressing. Nothing new to report.
Graybox framework testing prototype.
Also a bugfix for lower kernels. The kernel used to not have a function I was relying on.
moved jool_skb_cb initialization on IPv6 after all fragments packet arrived to the fragment database of jool, but we still init some skb stuff before the fragment database.
Merge branch 'issue41' into ipv6_db

Conflicts:
	mod/ttp/4to6.c