mac80211: fix nested sdata lock for IBSS/CSA

This fixes a regression introduced by my patch "mac80211: don't cancel
csa finalize work within stop_ap", which added sdata locks to
ieee80211_csa_finalize_work() without removing the locking for
ieee80211_ibss_finish_csa(), which is called by the former, resulting
in a deadlock due to nested locking.

Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/ibss.c

@@ -534,7 +534,8 @@ int ieee80211_ibss_finish_csa(struct ieee80211_sub_if_data *sdata)
 	int err;
 	u16 capability;
 
-	sdata_lock(sdata);
+	sdata_assert_lock(sdata);
+
 	/* update cfg80211 bss information with the new channel */
 	if (!is_zero_ether_addr(ifibss->bssid)) {
 		capability = WLAN_CAPABILITY_IBSS;
@@ -559,7 +560,6 @@ int ieee80211_ibss_finish_csa(struct ieee80211_sub_if_data *sdata)
 
 	/* generate the beacon */
 	err = ieee80211_ibss_csa_beacon(sdata, NULL);
-	sdata_unlock(sdata);
 	if (err < 0)
 		return err;