wifi: mac80211: add/use ieee80211_get_sn()

This will also be useful for MLO duplicate multicast
detection, but add it already here and use it in one
place that trivially converts.

Link: https://msgid.link/20240129200456.f0ff49c80006.I850d2785ab1640e56e262d3ad7343b87f6962552@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

include/linux/ieee80211.h

@@ -9,7 +9,7 @@
  * Copyright (c) 2006, Michael Wu <flamingice@sourmilk.net>
  * Copyright (c) 2013 - 2014 Intel Mobile Communications GmbH
  * Copyright (c) 2016 - 2017 Intel Deutschland GmbH
- * Copyright (c) 2018 - 2023 Intel Corporation
+ * Copyright (c) 2018 - 2024 Intel Corporation
  */
 
 #ifndef LINUX_IEEE80211_H
@@ -808,6 +808,11 @@ static inline bool ieee80211_is_frag(struct ieee80211_hdr *hdr)
 	       hdr->seq_ctrl & cpu_to_le16(IEEE80211_SCTL_FRAG);
 }
 
+static inline u16 ieee80211_get_sn(struct ieee80211_hdr *hdr)
+{
+	return le16_get_bits(hdr->seq_ctrl, IEEE80211_SCTL_SEQ);
+}
+
 struct ieee80211s_hdr {
 	u8 flags;
 	u8 ttl;

net/mac80211/rx.c

@@ -6,7 +6,7 @@
  * Copyright 2007-2010	Johannes Berg <johannes@sipsolutions.net>
  * Copyright 2013-2014  Intel Mobile Communications GmbH
  * Copyright(c) 2015 - 2017 Intel Deutschland GmbH
- * Copyright (C) 2018-2023 Intel Corporation
+ * Copyright (C) 2018-2024 Intel Corporation
  */
 
 #include <linux/jiffies.h>
@@ -1251,8 +1251,7 @@ static bool ieee80211_sta_manage_reorder_buf(struct ieee80211_sub_if_data *sdata
 {
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 	struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
-	u16 sc = le16_to_cpu(hdr->seq_ctrl);
-	u16 mpdu_seq_num = (sc & IEEE80211_SCTL_SEQ) >> 4;
+	u16 mpdu_seq_num = ieee80211_get_sn(hdr);
 	u16 head_seq_num, buf_size;
 	int index;
 	bool ret = true;