mac80211: remove supported channels element in 6 GHz if ECSA support

mac80211: remove supported channels element in 6 GHz if ECSA support

We should not include the supported channels element if we have
(advertise) support for extended channel switching. To avoid any
interop issues because we always added it in the past, obey this
restriction only in the (new) 6 GHz band.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/20200131113111.893106-1-luca@coelho.fi
Signed-off-by: Johannes Berg <johannes.berg@intel.com>