rt2x00: do not generate seqno in h/w if QOS is disabled

This is workaround H/W or F/W bug, see in code comments. Without the fix
ping can receive duplicated ICMP frames while associated with legacy AP.
Reported-by: Walter Goldens <goldenstranger@yahoo.com>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00.h

@@ -693,6 +693,7 @@ enum rt2x00_state_flags {
 	CONFIG_CHANNEL_HT40,
 	CONFIG_POWERSAVING,
 	CONFIG_HT_DISABLED,
+	CONFIG_QOS_DISABLED,
 
 	/*
 	 * Mark we currently are sequentially reading TX_STA_FIFO register

drivers/net/wireless/rt2x00/rt2x00mac.c

@@ -709,8 +709,18 @@ void rt2x00mac_bss_info_changed(struct ieee80211_hw *hw,
 			rt2x00dev->intf_associated--;
 
 		rt2x00leds_led_assoc(rt2x00dev, !!rt2x00dev->intf_associated);
+
+		clear_bit(CONFIG_QOS_DISABLED, &rt2x00dev->flags);
 	}
 
+	/*
+	 * Check for access point which do not support 802.11e . We have to
+	 * generate data frames sequence number in S/W for such AP, because
+	 * of H/W bug.
+	 */
+	if (changes & BSS_CHANGED_QOS && !bss_conf->qos)
+		set_bit(CONFIG_QOS_DISABLED, &rt2x00dev->flags);
+
 	/*
 	 * When the erp information has changed, we should perform
 	 * additional configuration steps. For all other changes we are done.

drivers/net/wireless/rt2x00/rt2x00queue.c

@@ -213,8 +213,19 @@ static void rt2x00queue_create_tx_descriptor_seq(struct rt2x00_dev *rt2x00dev,
 
 	__set_bit(ENTRY_TXD_GENERATE_SEQ, &txdesc->flags);
 
-	if (!test_bit(REQUIRE_SW_SEQNO, &rt2x00dev->cap_flags))
-		return;
+	if (!test_bit(REQUIRE_SW_SEQNO, &rt2x00dev->cap_flags)) {
+		/*
+		 * rt2800 has a H/W (or F/W) bug, device incorrectly increase
+		 * seqno on retransmited data (non-QOS) frames. To workaround
+		 * the problem let's generate seqno in software if QOS is
+		 * disabled.
+		 */
+		if (test_bit(CONFIG_QOS_DISABLED, &rt2x00dev->flags))
+			__clear_bit(ENTRY_TXD_GENERATE_SEQ, &txdesc->flags);
+		else
+			/* H/W will generate sequence number */
+			return;
+	}
 
 	/*
 	 * The hardware is not able to insert a sequence number. Assign a