wifi: nl80211: document channel opmode change channel width

wifi: nl80211: document channel opmode change channel width

The opmode change notification is entirely unused by existing
userspace except for printing out the values. As such, there's
no need to keep it perfectly accurate, and the implementation
in mac80211 doesn't report it correctly today. Add a note in
the documentation that it may not differentiate 80+80 and 160.

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20260415144514.87d5b1ce688f.Ia9a0769d52dcfe56f7b0dff903ed14db3ef04920@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>