wifi: mac80211: optionally pass chandef to ieee80211_sta_cur_vht_bw()

We'll need this as well for channel switching cases, so
add the ability now to pass the chandef to calculate for.

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20240612143418.f70e05d9f306.Ifa0ce267de4f0ef3c21d063fb0cbf50e84d7d6ff@changeid


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