Switching between half-duplex and full duplex

[Pang]

Hello,
  I have just installed FreeBSD and found that the nic em0 is set to 
half-duplex only. Could anyone tell me how I can switch it to full-duplex?

em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=b<RXCSUM,TXCSUM,VLAN_MTU>
        inet 172.16.0.2 netmask 0xfffffffc broadcast 172.16.0.1
        ether XX:XX:XX:XX:XX:XX
        media: Ethernet autoselect (10baseT/UTP <half-duplex>)
        status: active

Thanks
Pang