FWIW I couldn't get my pci netgear ga311 to be flagged as built in either. Gave up an re-enabled the mobo lan, and set that as built in. Now have two network intefaces, but that seems the only way to go.
Yes, i added that Method. It appears as LAN, i just changed Device ethernet to LAN before posting. Only problem is that the built-in flag just is not set