mac80211: let the driver reserve extra tailroom in beacons

Can be used to add extra IEs (such as P2P NoA) without having to
reallocate the buffer.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 6d59e21..002ded2 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -2549,7 +2549,8 @@
 			 */
 			skb = dev_alloc_skb(local->tx_headroom +
 					    beacon->head_len +
-					    beacon->tail_len + 256);
+					    beacon->tail_len + 256 +
+					    local->hw.extra_beacon_tailroom);
 			if (!skb)
 				goto out;
 
@@ -2581,7 +2582,8 @@
 			ieee80211_update_csa(sdata, presp);
 
 
-		skb = dev_alloc_skb(local->tx_headroom + presp->head_len);
+		skb = dev_alloc_skb(local->tx_headroom + presp->head_len +
+				    local->hw.extra_beacon_tailroom);
 		if (!skb)
 			goto out;
 		skb_reserve(skb, local->tx_headroom);
@@ -2608,7 +2610,8 @@
 		skb = dev_alloc_skb(local->tx_headroom +
 				    bcn->head_len +
 				    256 + /* TIM IE */
-				    bcn->tail_len);
+				    bcn->tail_len +
+				    local->hw.extra_beacon_tailroom);
 		if (!skb)
 			goto out;
 		skb_reserve(skb, local->tx_headroom);