staging: vt6656: use NULLFUCTION stack on mac80211

BugLink: https://bugs.launchpad.net/bugs/1864774

commit d579c43c upstream.

It appears that the drivers does not go into power save correctly the
NULL data packets are not being transmitted because it not enabled
in mac80211.

The driver needs to capture ieee80211_is_nullfunc headers and
copy the duration_id to it's own duration data header.

Cc: stable <stable@vger.kernel.org>
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Link: https://lore.kernel.org/r/610971ae-555b-a6c3-61b3-444a0c1e35b4@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/staging/vt6656/main_usb.c

@@ -1002,6 +1002,7 @@ vt6656_probe(struct usb_interface *intf, const struct usb_device_id *id)
 	ieee80211_hw_set(priv->hw, RX_INCLUDES_FCS);
 	ieee80211_hw_set(priv->hw, REPORTS_TX_ACK_STATUS);
 	ieee80211_hw_set(priv->hw, SUPPORTS_PS);
+	ieee80211_hw_set(priv->hw, PS_NULLFUNC_STACK);
 
 	priv->hw->max_signal = 100;
 

drivers/staging/vt6656/rxtx.c

@@ -280,11 +280,9 @@ static u16 vnt_rxtx_datahead_g(struct vnt_usb_send_context *tx_context,
 							PK_TYPE_11B, &buf->b);
 
 	/* Get Duration and TimeStamp */
-	if (ieee80211_is_pspoll(hdr->frame_control)) {
-		__le16 dur = cpu_to_le16(priv->current_aid | BIT(14) | BIT(15));
-
-		buf->duration_a = dur;
-		buf->duration_b = dur;
+	if (ieee80211_is_nullfunc(hdr->frame_control)) {
+		buf->duration_a = hdr->duration_id;
+		buf->duration_b = hdr->duration_id;
 	} else {
 		buf->duration_a = vnt_get_duration_le(priv,
 						tx_context->pkt_type, need_ack);
@@ -373,10 +371,8 @@ static u16 vnt_rxtx_datahead_ab(struct vnt_usb_send_context *tx_context,
 			  tx_context->pkt_type, &buf->ab);
 
 	/* Get Duration and TimeStampOff */
-	if (ieee80211_is_pspoll(hdr->frame_control)) {
-		__le16 dur = cpu_to_le16(priv->current_aid | BIT(14) | BIT(15));
-
-		buf->duration = dur;
+	if (ieee80211_is_nullfunc(hdr->frame_control)) {
+		buf->duration = hdr->duration_id;
 	} else {
 		buf->duration = vnt_get_duration_le(priv, tx_context->pkt_type,
 						    need_ack);