Back port "scan_freq" implementation to wpa supplicant 0.6.x

[alfred steele]

> Err, I think that could be misunderstood -- the kernel has WEXT/cfg80211
> compat code so that you can use new kernel drivers like drivers based on
> mac80211 with old tools like iwconfig/wpa_supplicant -Dwext --
> nl80211-based tools like iw/wpa_supplicant -Dnl80211 can only be used
> with drivers that are implemented to the cfg80211 APIs.
Can i use "scan_freq" with wpa_supplicant -Dnl80211 against kernel
version 2.6.26 since it does not seem to have any trace of cfg80211?

Thanks,
Alfred