mac80211: use ieee80211_bss_get_elem()

Instead of ieee80211_bss_get_ie(), use the more typed
ieee80211_bss_get_elem().

Link: https://lore.kernel.org/r/20211220113609.56f8e2a70152.Id5a56afb8a4f9b38d10445e5a1874e93e84b5251@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mlme.c

@@ -4906,7 +4906,7 @@ static u8 ieee80211_ht_vht_rx_chains(struct ieee80211_sub_if_data *sdata,
 				     struct cfg80211_bss *cbss)
 {
 	struct ieee80211_if_managed *ifmgd = &sdata->u.mgd;
-	const u8 *ht_cap_ie, *vht_cap_ie;
+	const struct element *ht_cap_elem, *vht_cap_elem;
 	const struct ieee80211_ht_cap *ht_cap;
 	const struct ieee80211_vht_cap *vht_cap;
 	u8 chains = 1;
@@ -4914,9 +4914,9 @@ static u8 ieee80211_ht_vht_rx_chains(struct ieee80211_sub_if_data *sdata,
 	if (ifmgd->flags & IEEE80211_STA_DISABLE_HT)
 		return chains;
 
-	ht_cap_ie = ieee80211_bss_get_ie(cbss, WLAN_EID_HT_CAPABILITY);
-	if (ht_cap_ie && ht_cap_ie[1] >= sizeof(*ht_cap)) {
-		ht_cap = (void *)(ht_cap_ie + 2);
+	ht_cap_elem = ieee80211_bss_get_elem(cbss, WLAN_EID_HT_CAPABILITY);
+	if (ht_cap_elem && ht_cap_elem->datalen >= sizeof(*ht_cap)) {
+		ht_cap = (void *)ht_cap_elem->data;
 		chains = ieee80211_mcs_to_chains(&ht_cap->mcs);
 		/*
 		 * TODO: use "Tx Maximum Number Spatial Streams Supported" and
@@ -4927,12 +4927,12 @@ static u8 ieee80211_ht_vht_rx_chains(struct ieee80211_sub_if_data *sdata,
 	if (ifmgd->flags & IEEE80211_STA_DISABLE_VHT)
 		return chains;
 
-	vht_cap_ie = ieee80211_bss_get_ie(cbss, WLAN_EID_VHT_CAPABILITY);
-	if (vht_cap_ie && vht_cap_ie[1] >= sizeof(*vht_cap)) {
+	vht_cap_elem = ieee80211_bss_get_elem(cbss, WLAN_EID_VHT_CAPABILITY);
+	if (vht_cap_elem && vht_cap_elem->datalen >= sizeof(*vht_cap)) {
 		u8 nss;
 		u16 tx_mcs_map;
 
-		vht_cap = (void *)(vht_cap_ie + 2);
+		vht_cap = (void *)vht_cap_elem->data;
 		tx_mcs_map = le16_to_cpu(vht_cap->supp_mcs.tx_mcs_map);
 		for (nss = 8; nss > 0; nss--) {
 			if (((tx_mcs_map >> (2 * (nss - 1))) & 3) !=