Revert "cfg80211: Use 5MHz bandwidth by default when checking usable channels"

This reverts commit 8eca1fb6.

Felix notes that this broke regulatory, leaving channel 12 open for AP
operation in the US regulatory domain where it isn't permitted.

Link: http://mid.gmane.org/53A6C0FF.9090104@openwrt.org


Reported-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>