[gPXE] Persist config with gPXE

[Stefan Hajnoczi]

RTL8139 and Level 5 Etherfabric support non-volatile options.  This
feature is not widely available in gPXE, most drivers do not support
it.

There is no list of "preferred" NICs but you can check for all
supported NIC families on ROM-o-matic "Choose a NIC type" list:
http://rom-o-matic.net/gpxe/gpxe-git/gpxe.git/contrib/rom-o-matic/

Or on the #etherboot IRC Freenode channel with the following command:
gpxebot: lspci 10ec 8139
(where 10ec:8139 is the PCI ID of the NIC you want to check.)

Stefan