I noticed this problem some time ago and decided it'd be good to document it here, so here goes:
As recently as the 20170907 release of Libreboot, GA-G41M-ES2L has a bug which appears to require the MAC address be hardcoded into the ROM file itself. Reference from https://libreboot.org/docs/install/ga-g41m-es2l.html :
NOTE: due to a bug in the hardware, the MAC address is hardcoded in coreboot-libre. Therefore, you must set your own MAC address in your operating system.
This has (at least) one important practical implication in that this hardcoded address is the only one which responds to magic packets to wake up the system from various states of sleep.
Since the hardcoded MAC address is the same for all Libreboot-distributed copies of this ROM, this could be especially problematic if two or more GA-G41M-ES2Ls are in the same network broadcast area. It would seem the only way to resolve this issue is to change the hardcoded MAC address and rebuild coreboot, but I'm open to more flexible suggestions on how to remedy the situation.
@swiftgeek wanted me to mention that this device doesn't have a flash descriptor, which I presume affects our options for resolving this bug.
I semi-fixed this ages ago in coreboot. It requires the desired MAC address to be stored as a file in CBFS, but cannot autodetect the factory one.