mac80211: mesh: separate plid and aid concepts

According to 802.11-2012 13.3.1, a mesh STA should assign an AID
upon receipt of a mesh peering open frame rather than using the link
id of the peer.  Using the peer link id has two potential issues:
it may not be unique among the peers, and by its nature it is random,
so the TIM may not compress well.

In preparation for allocating it properly, use sta->sta.aid, but keep
the existing behavior of using the plid in the aid we send.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.h

@@ -277,6 +277,7 @@ struct ieee80211_fast_tx {
  * @plink_lock: serialize access to plink fields
  * @llid: Local link ID
  * @plid: Peer link ID
+ * @aid: local aid supplied by peer
  * @reason: Cancel reason on PLINK_HOLDING state
  * @plink_retries: Retries in establishment
  * @plink_state: peer link state
@@ -301,6 +302,7 @@ struct mesh_sta {
 	spinlock_t plink_lock;
 	u16 llid;
 	u16 plid;
+	u16 aid;
 	u16 reason;
 	u8 plink_retries;