Comment 22 for bug 275227

static inline struct ieee80211_sub_if_data *
IEEE80211_DEV_TO_SUB_IF(struct net_device *dev)
{
        struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);

        BUG_ON(!local || local->mdev == dev);

        return netdev_priv(dev);
}