Hello,

Here are the an(4) driver radiotap patches,
they are located at :

http://jard.in/~rival/netbsd/radiotap_an.tgz

Apply the patches on each file and recompile
your kernel, then use tcpdump -y IEEE802_11_RADIO

I guess they are far from perfect, but any comments/feedback
is appreciated.

Hope it helps,
Eric.