wifi: cfg80211: improve supported_selector documentation

Improve the documentation for supported BSS selectors to make it more
precise.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Reviewed-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250308225541.ba402ff47314.I502b56111b62ea0be174ae76bd03684ae1d4aefb@changeid


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