root@OpenWrt:/mnt/remote# airodump-ng --channel 6 --write Mar08 wl0

ARP linktype is set to 1 (Ethernet) - expected ARPHRD_IEEE80211
or ARPHRD_IEEE80211_PRISM instead.  Make sure RFMON is enabled:
run 'ifconfig wl0 up; iwconfig wl0 mode Monitor channel <#>'

root@OpenWrt:/mnt/remote# iwconfig wl0
wl0       IEEE 802.11-DS  ESSID:""
          Mode:Monitor  Frequency:2.437 GHz  Tx-Power:19 dBm
          RTS thr:2347 B   Fragment thr:2346 B
          Encryption key:off