wpi, iwn: implement ic_getradiocaps method

[avos]

Summary

This will allow to restore channel list after switching interface to more restrictive regdomain.

An example:

1. ifconfig wlan0 down
2. ifconfig wlan0 list chan

Channel 1 : 2412 MHz 11g Channel 8 : 2447 MHz 11g
Channel 2 : 2417 MHz 11g Channel 9 : 2452 MHz 11g
Channel 3 : 2422 MHz 11g Channel 10 : 2457 MHz 11g
Channel 4 : 2427 MHz 11g Channel 11 : 2462 MHz 11g
Channel 5 : 2432 MHz 11g Channel 12 : 2467* MHz 11g
Channel 6 : 2437 MHz 11g Channel 13 : 2472* MHz 11g
Channel 7 : 2442 MHz 11g

3. ifconfig wlan0 regdomain FCC country US
4. ifconfig wlan0 list chan

Channel 1 : 2412 MHz 11g Channel 7 : 2442 MHz 11g
Channel 2 : 2417 MHz 11g Channel 8 : 2447 MHz 11g
Channel 3 : 2422 MHz 11g Channel 9 : 2452 MHz 11g
Channel 4 : 2427 MHz 11g Channel 10 : 2457 MHz 11g
Channel 5 : 2432 MHz 11g Channel 11 : 2462 MHz 11g
Channel 6 : 2437 MHz 11g

5. ifconfig wlan0 regdomain NONE country UA
6. ifconfig wlan0 list chan

Channel 1 : 2412 MHz 11g Channel 7 : 2442 MHz 11g
Channel 2 : 2417 MHz 11g Channel 8 : 2447 MHz 11g
Channel 3 : 2422 MHz 11g Channel 9 : 2452 MHz 11g
Channel 4 : 2427 MHz 11g Channel 10 : 2457 MHz 11g
Channel 5 : 2432 MHz 11g Channel 11 : 2462 MHz 11g
Channel 6 : 2437 MHz 11g <<< 12 and 13 channels are missing

Test Plan

Tested with Intel 3945BG only.

[adrian]

looks good to me!