mac80211: TDLS: don't require beaconing for AP BW

Stop downgrading TDLS chandef when reaching the AP BW. The AP provides
the necessary regulatory protection in this case.

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=153961

, which
reported an infinite loop here.

Reported-by: Kamil Toman <kamil.toman@gmail.com>
Signed-off-by: Arik Nemtsov <arikx.nemtsov@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>