Teach the 802.11 printer about Channel Switch Announcements (advertised by

Teach the 802.11 printer about Channel Switch Announcements (advertised by
an AP in beacons in the run-up to a channel switch, either for radar avoidance,
or for frequency management). ok stsp@

We don't support these in net80211 yet (as pointed out by stsp a few days ago)
but it's useful to at least have a way to debug why your connection is getting
knocked down!