wifi: mac80211: allow CSA to same channel

This could be used e.g. for temporarily sending quiet
(mode=1 in CSA/ECSA), or updating bandwidth. This is
also useful for testing, since it's something that an
AP may do and the client needs to be prepared. Simply
allow it.

Link: https://msgid.link/20240129203544.ef7258d5790d.Idafe22e41621757458d4960659b9621853f7104d@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>