Update tcp_logging to have two new features

[rrs]

Summary

This update has been running in NF for some time. It adds two features:

1. The ability to add an added bit of text in the log - which is more cosmetic.

and

2. The ability from a sysctl to turn off all logging. This is an important security consideration. I.e. if you are under attack having the ability to turn off all excess activity (such as logging) becomes a "good" thing to have.

Test Plan

Easiest way to test this is to run a few tcp connections and
turn on the logging and pull out the logs. If you get logs
it's working. One can also use the sysctl to truncate logging
and validate that it stops all logging. The cosmetic feature
can also be tested by simply using it and validating it
shows up in the new logging format.