wifi: cfg80211: detect stuck ECSA element in probe resp

In the Linux kernel, the following vulnerability has been resolved:

wifi: cfg80211: detect stuck ECSA element in probe resp

We recently added some validation that we don't try to
connect to an AP that is currently in a channel switch
process, since that might want the channel to be quiet
or we might not be able to connect in time to hear the
switching in a beacon. This was in commit c09c4f31998b
("wifi: mac80211: don't connect to an AP while it's in
a CSA process").

However, we promptly got a report that this caused new
connection failures, and it turns out that the AP that
we now cannot connect to is permanently advertising an
extended channel switch announcement, even with quiet.
The AP in question was an Asus RT-AC53, with firmware
3.0.0.4.380_10760-g21a5898.

As a first step, attempt to detect that we're dealing
with such a situation, so mac80211 can use this later.