docs: Make MACs lowercase in network config (SC-541)

[TheRealFalcon]

Proposed Commit Message

docs: Make MACs lowercase in network config

LP: #1876941

Additional Context

Test Steps

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[holmanb]

I grepped a bit for other spots we might need to update ((:.*){6}) and I didn't find anything. There are a few tests that have uppercase mac addresses, but those look to be mocking output from system commands, so no need to change those. LGTM