So, you want to do kernel programming. Great.
That means you have to first seriously learn C. Write at least 10,000 lines of functioning C code. Get it reviewed and critiqued by experts. Make sure it's production worthy. This will probably take you half a year, working 20% of your time. Sorry, but owning one book is just a tiny step into a very long voyage there.
Then learn about the kernel. Read the book SirDice recommended, and understand it. Ask someone to give you a little quiz, and make sure you can do the quizzes. Honestly, I would also read a good undergraduate operating systems textbook, like Tanenbaum, and do the homework problems. That's like taking a 1-semester undergraduate OS class; again 20% of your time for half a year.
You want to work on the network part? For that, you need to understand how networking works. The fact that you ask "the part that connects to the internet" shows that you have no clue about that. There are oodles of TCP/IP books. Get one, understand it.
Once you have done these things, the question of "where is the source code" will be irrelevant, and you will know the answer.
I don't think you even understand the complexity of the question you have asked.