I had success flashing an iPXE rom on the NIC mentioned above. lspci output: 41:00.0 Ethernet controller : Intel Corporation 82599 10 Gigabit Network Connection [8086:1557] (rev 01)
df@mobilex:~/nfs-home/Dokumente/iPXE/Intel Corporation 82599 10 Gigabit$ sudo flashrom -p nicintel_spi:pci=41:00.0 -w ipxe.rom flashrom v0.9.9-r1954 on Linux 5.3.0-46-generic (x86_64) flashrom is free software, get the source code at https://flashrom.org
Calibrating delay loop... OK. === This PCI device is UNTESTED. Please report the 'flashrom -p xxxx' output to firstname.lastname@example.org if it works for you. Please add the name of your PCI device to the subject. Thank you for your help! === Found Winbond flash chip "W25X40" (512 kB, SPI) on nicintel_spi. Reading old flash chip contents... done. Erasing and writing flash chip... Erase/write done. Verifying flash... VERIFIED.