Fix OSI Model links

[guardrex]

Links to https://osi-model.com are broken. I have an idea 🤔💡 on how to fix these.

[guardrex]

Yikes! 🙈 That site has been HACKED, too. Don't LOOK! 👀 There's a bunch of evil crap on that site now. Yeah, we need to get rid of these links.

I'll find an alternative or define the few terms needed in the text.