wl12xx: use round-robin policy for tx

Currently, a single vif might starve all the other vifs.
Save the last vif we dequeued a packet from, and continue
with the following one using a round-robin policy.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>
diff --git a/drivers/net/wireless/wl12xx/main.c b/drivers/net/wireless/wl12xx/main.c
index 6e6ac63f..f29d18d 100644
--- a/drivers/net/wireless/wl12xx/main.c
+++ b/drivers/net/wireless/wl12xx/main.c
@@ -2282,6 +2282,8 @@
 
 	wl12xx_tx_reset_wlvif(wl, wlvif);
 	wl1271_free_ap_keys(wl, wlvif);
+	if (wl->last_wlvif == wlvif)
+		wl->last_wlvif = NULL;
 	list_del(&wlvif->list);
 	memset(wlvif->ap.sta_hlid_map, 0, sizeof(wlvif->ap.sta_hlid_map));
 	wlvif->role_id = WL12XX_INVALID_ROLE_ID;