WDS interface always busy, cannot be brought up

[Neil Hellfeldt <hellfeldt@esteem.com>]

commit 65a124dd719d6e90591e4756bb04e1719489705e prevents WDS interface 
type from bring brought up.

Simple Test:
before this you must have a AP interface, I used hostapd to create it so 
I don't have a single liner to show that.

iw dev wlan0 interface add wlan0wds0 type wds
ip link set dev wlan0wds0 address 00:11:22:33:44:55
iw dev wlan0wds0 set peer 00:66:77:88:99:AA
ifconfig wlan0wds0 up

Konsole output ifconfig: SIOCSIFFLAGS: Device or resource busy

The commit: says it checks for channel availability.

WDS do not use there own channels. They use the channel of the ap 
interface that already exists,
because of this cfg80211_check_combinations will always return -EBUSY.

That do to this test statement
     if (num == 0)
         return -EBUSY;