TFTP boot: warn users about network hardware incompatibility

[jvsalo]

I believe the tutorial page https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/net_tutorial.md deserves a mention about the incompatibility of networking hardware.

I know it's mentioned here https://www.raspberrypi.org/blog/pi-3-booting-part-ii-ethernet-all-the-awesome/ but to save other peoples' time I would certainly mention it on the main tutorial page.

It can be frustrating to debug why nothing works, if the R-Pi firmware has trouble negotiating link with the switch/computer on the other end.

Most of my networking hardware was incompatible, finally got hold of HP 1810-24G that worked.

[jvsalo]

Disabling STP frames in the network worked wonders, by the way.

[JamesH65]

@ghollingworth Any thoughts Gordon?

[JamesH65]

ping @ghollingworth

[ghollingworth]

I do not have suitable hardware to test this on, so would only be adding, YMMV

If you have some specific examples of switches that do not work can you add a note as a pull request?

Thanks

[JamesH65]

fixed by #983

[JamesH65]

Fix merged.