firewall: More space for custom rules.

Creating space for custom rules, so we do not enforce connection
tracking handling for every package in 001. Therefore chain creation is
moved into a new file, so custom rule can jump packages to the post
processing chains.
firewall: Utility chain for debug logging.

So we can log dropped packages, if we like.
Merge pull request #69 from sargon/firewall

Some firewall enhancements