Make ieee80211_chan_bw_change() able to use the reserved chanreq
(really the chandef part of it) for the calculations, so it can
be used _without_ applying the changes first. Remove the comment
that indicates this is required, since it no longer is. However,
this capability only gets used later.

Also, this is not ideal, we really should not different so much
between reserved and non-reserved usage, to simplify. That's a
further cleanup later though.
Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20240612143418.1a08cf83b8cb.Ie567bb272eb25ce487651088f13ad041f549651c@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>