wifi: rtl8xxxu: prepare supporting two virtual interfaces

To prepare for concurrent mode, add an array ("vifs") to rtl8xxxu_priv
to keep track of both interfaces.

Keep the old priv->vif as long there are still users of it and let
priv->vifs[0] point to the same location.
Signed-off-by: Martin Kaistra <martin.kaistra@linutronix.de>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20231222101442.626837-3-martin.kaistra@linutronix.de

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu.h

@@ -1897,6 +1897,8 @@ struct rtl8xxxu_priv {
 	 * is supported and no iface_combinations are provided.
 	 */
 	struct ieee80211_vif *vif;
+
+	struct ieee80211_vif *vifs[2];
 	struct delayed_work ra_watchdog;
 	struct work_struct c2hcmd_work;
 	struct sk_buff_head c2hcmd_queue;

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c

@@ -6569,10 +6569,12 @@ static int rtl8xxxu_add_interface(struct ieee80211_hw *hw,
 	int ret;
 	u8 val8;
 
-	if (!priv->vif)
+	if (!priv->vif) {
 		priv->vif = vif;
-	else
+		priv->vifs[0] = vif;
+	} else {
 		return -EOPNOTSUPP;
+	}
 
 	switch (vif->type) {
 	case NL80211_IFTYPE_STATION:
@@ -6622,8 +6624,10 @@ static void rtl8xxxu_remove_interface(struct ieee80211_hw *hw,
 
 	dev_dbg(&priv->udev->dev, "%s\n", __func__);
 
-	if (priv->vif)
+	if (priv->vif) {
 		priv->vif = NULL;
+		priv->vifs[0] = NULL;
+	}
 }
 
 static int rtl8xxxu_config(struct ieee80211_hw *hw, u32 changed)