Explicitly call-out Vendor Class identifier for PXE

[virtualjmills]

Vendor Class identifier was buried in some tcpdump parsed output further down in the page. Explicitly calling it out up-top, in some environments this is used as an initial pass filter by the DHCP server to determine which set of responses / behavior to use when interacting with the PXE Client system.

[lurch]

Is this the same for network-booting on both a Pi 3B+ and also a Pi 4B ?
ping @timg236

[timg236]

Same on pi4

[JamesH65]

@timg236 Are you OK with this change? Seems sane to me.

[timg236]

The ROM doesn't do TFTP boot on Pi4 although the behaviour is the same in bootloader. I think this page is really about Pi3 ROM

[lurch]

I wonder if that page needs to be "refactored" slightly to show which parts of the net-boot process are different between Pi3 ROM and Pi4 EEPROM (e.g. Pi4 EEPROM probably doesn't request bootcode.bin?), and which parts are common to both? 🤷

[aallan]

I'd encourage you to wrap this PR up in the next week or so as we're in the process of transitioning the documentation from the current Markdown-based source format to Asciidoc. At some point soon — probably around the end of June, beginning of July — we will freeze the current documentation repo. After that time contributions and PRs based on the Markdown source will not be accepted, and any PRs that are still open will be closed.

See #1911 for full details.

[timg236]

ok to merge