target=0
for file in /sys/class/net/*; do
    if [ ! -f /sys/class/net/$(basename $file)/wireless ] -a [ "$(< /sys/class/net/$(basename $file)/operstate)" -eq 'up' ]; then
        if [ $target -eq 0 ]; then
            debconf-set netcfg/choose_interface $(basename $file)
        fi
        target=$(basename $file)
    fi
done