mac80211: add TX fastpath

In order to speed up mac80211's TX path, add the "fast-xmit" cache
that will cache the data frame 802.11 header and other data to be
able to build the frame more quickly. This cache is rebuilt when
external triggers imply changes, but a lot of the checks done per
packet today are simplified away to the check for the cache.

There's also a more detailed description in the code.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.c

@@ -1201,6 +1201,8 @@ void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
 	ps_dbg(sdata,
 	       "STA %pM aid %d sending %d filtered/%d PS frames since STA not sleeping anymore\n",
 	       sta->sta.addr, sta->sta.aid, filtered, buffered);
+
+	ieee80211_check_fast_xmit(sta);
 }
 
 static void ieee80211_send_null_response(struct ieee80211_sub_if_data *sdata,
@@ -1599,6 +1601,7 @@ void ieee80211_sta_block_awake(struct ieee80211_hw *hw,
 
 	if (block) {
 		set_sta_flag(sta, WLAN_STA_PS_DRIVER);
+		ieee80211_clear_fast_xmit(sta);
 		return;
 	}
 
@@ -1616,6 +1619,7 @@ void ieee80211_sta_block_awake(struct ieee80211_hw *hw,
 		ieee80211_queue_work(hw, &sta->drv_deliver_wk);
 	} else {
 		clear_sta_flag(sta, WLAN_STA_PS_DRIVER);
+		ieee80211_check_fast_xmit(sta);
 	}
 }
 EXPORT_SYMBOL(ieee80211_sta_block_awake);
@@ -1720,6 +1724,7 @@ int sta_info_move_state(struct sta_info *sta,
 			     !sta->sdata->u.vlan.sta))
 				atomic_dec(&sta->sdata->bss->num_mcast_sta);
 			clear_bit(WLAN_STA_AUTHORIZED, &sta->_flags);
+			ieee80211_clear_fast_xmit(sta);
 		}
 		break;
 	case IEEE80211_STA_AUTHORIZED:
@@ -1729,6 +1734,7 @@ int sta_info_move_state(struct sta_info *sta,
 			     !sta->sdata->u.vlan.sta))
 				atomic_inc(&sta->sdata->bss->num_mcast_sta);
 			set_bit(WLAN_STA_AUTHORIZED, &sta->_flags);
+			ieee80211_check_fast_xmit(sta);
 		}
 		break;
 	default: