mac80211: continue using disabled channels while connected

In case the AP has different regulatory information than we do,
it can happen that we connect to an AP based on e.g. the world
roaming regulatory data, and then update our database with the
AP's country information disables the channel the AP is using.
If this happens on an HT AP, the bandwidth tracking code will
hit the WARN_ON() and disconnect. Since that's not very useful,
ignore the channel-disable flag in bandwidth tracking.

Cc: stable@vger.kernel.org
Reported-by: Chris Wright <chrisw@sous-sol.org>
Tested-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>