8.0-BETA3: Cannot use iwn on Thinkpad R61

I was trying today to get 8.0-BETA3 amd64 usable on my laptop (Thinkpad
R61, Intel 4965 wireless chipset) and so far have had no success.  iwnfw
and if_iwn load without errors, but when I do

# ifconfig iwn0 list caps

it fails with "invalid argument."  Similarly, wpa_supplicant cannot
initialize the interface (again reporting invalid argument).  `ifconfig
iwn0 up scan` also fails, complaining that it cannot get the scan results=
=2E

Any suggestions?

- Michael