I'm running into one of the known netbooting bugs. I can't boot the rpi 3 unless I put the bootcode.bin on the SD card. Fetching over the network is not possible. The rpi is directly connected to a mainboard which hosts the tftp server but it seems the interface on the server does not come up fast enough when the rpi is booting.
Is there anything I can do either on the server or on the rpi side so that also bootcode.bin gets loaded over the network?
Could maybe the firmware be changed so it does an dhcp request more often? This is often the case when you use a normal bios or ipxe for netbooting computers.