> Could you please define what "roaming mode" actually does?
> Does it involve changes of ESSIDs, or changes of BSSIDs,
> or something else?

prism2 chip have three roaming mode, roaming decision made by CW10
firmware, by host and disable.
If set 1, all roaming is handled by firmware, we do nothing.
if set 2, host be interrupt with ScanRequest when either PRISM MAC 
scans or host initiates a scan. Then, Host do JoinRequest at that
time. But this mode is not obstructed by present wi(4) code.