mac80211: make scan_sdata pointer usable with RCU

Making the scan_sdata pointer usable with RCU makes
it possible to dereference it in the RX path to see
if a received frame actually matches the interface
that is scanning. This is just preparations, making
the pointer __rcu.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index c3241c3..9f2534a 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -972,7 +972,7 @@
 	unsigned long leave_oper_channel_time;
 	enum mac80211_scan_state next_scan_state;
 	struct delayed_work scan_work;
-	struct ieee80211_sub_if_data *scan_sdata;
+	struct ieee80211_sub_if_data __rcu *scan_sdata;
 	enum nl80211_channel_type _oper_channel_type;
 	struct ieee80211_channel *oper_channel, *csa_channel;