clear the options of the current media, i.e. only inherit the instance,
which matches what NetBSD does. Without this it's really non-intuitive
that the following sequence:
ifconfig bge0 media 1000baseT mediaopt full-duplex
ifconfig bge0 media 100baseTX
results in 100baseTX full-duplex to be set or that:
ifconfig bge0 media autoselect mediaopt flowcontrol
ifconfig bge0 media 1000baseT mediaopt full-duplex
tries to set 1000baseT full-duplex with flowcontrol, which isn't suported
und thus fails while the following:
ifconfig re0 media 1000baseT mediaopt flowcontrol,full-duplex
ifconfig re0 media autoselect
just switches to autoselection without flowcontrol.
MFC after: 2 weeks
6f135a7584