You can't manually fix the option on that card and if you do:
ifconfig -m nfe0
You will see the option for:
media 1000baseSX
media 1000baseSX mediaopt full-duplex
Witch are obviously wrong.
Also, some issue with the AMD64 mp kernel, make the box crash when you
push a lots of traffic to it.
Lots of comment in archive and tests as well. The i386 looks ok so far,
except the nfe still bad no matter what, however the AMD64 is not really
stable and if you put the ACPI on, well...
I have 4 of these and still sadly haven't put any in production yet
because of various stability issue with them.
So, I wouldn't put it as a router right now, but YMMV I guess.
Test well before you do.
Daniel