wifi: mt76: move struct ieee80211_chanctx_conf up to struct mt76_vif

Move struct ieee80211_chanctx_conf up to struct mt76_vif to allow the
connac2 library can access the struct ieee80211_chanctx_conf * member in
struct mt76_vif.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Reviewed-by: David Ruth <druth@chromium.org>
Tested-by: David Ruth <druth@chromium.org>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>