mac80211: add ieee80211_tx_prepare_skb() helper function

This can be used by a driver to prepare skbs for transmission, which were
obtained via functions such as ieee80211_probereq_get or
ieee80211_nullfunc_get.

This is useful for drivers that want to send those frames directly, but
need rate control information to be prepared first.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -4571,4 +4571,18 @@ void ieee80211_report_wowlan_wakeup(struct ieee80211_vif *vif,
 				    struct cfg80211_wowlan_wakeup *wakeup,
 				    gfp_t gfp);
 
+/**
+ * ieee80211_tx_prepare_skb - prepare an 802.11 skb for transmission
+ * @hw: pointer as obtained from ieee80211_alloc_hw()
+ * @vif: virtual interface
+ * @skb: frame to be sent from within the driver
+ * @band: the band to transmit on
+ * @sta: optional pointer to get the station to send the frame to
+ *
+ * Note: must be called under RCU lock
+ */
+bool ieee80211_tx_prepare_skb(struct ieee80211_hw *hw,
+			      struct ieee80211_vif *vif, struct sk_buff *skb,
+			      int band, struct ieee80211_sta **sta);
+
 #endif /* MAC80211_H */