cfg80211: ignore channel state for stopped AP/mesh interfaces

Without this change, running AP + station on the same wiphy
does not work since the commit "cfg80211: add channel checking
for iface combinations". The stopped AP prevents the client
from connecting to an AP on a different channel.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
[line-break commit message to < 72 chars]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>