Many thanks nzchris for your work!I decided to give this a go today, quickly realised that TrueNAS doesn't come with the tools required to compile the driver, so I installed FreeBSD 13.0 in a VirtualBox and compiled the driver there.
Copied it back to the NAS /boot/kernel and added the Tunable, and it is working on my N40L with TrueNAS 13.0.
Compiled driver attached.
I can confirm that your if_bge.ko file is the only file that works perfectly on HP Microserver N40L with the last version of truenas (TrueNAS-13.0-U3.1).
After copying the file on /boot/kernel and add the tunetable now from ifconfig -m bge0 I see all WOL features and the wake on lan feature works like a charm.
I'm new to FreeBSD environment, can you try explaining me how did yo do to compile this driver? Also in case of truenas version upgrade.
Many Thanks!
Marco