mac80211: check interface is down before type change

commit c1f9a764 upstream.

For some strange reason the netif_running() check
ended up after the actual type change instead of
before, potentially causing all kinds of problems
if the interface is up while changing the type;
one of the problems manifests itself as a warning:

WARNING: at net/mac80211/iface.c:651 ieee80211_teardown_sdata+0xda/0x1a0 [mac80211]()
Hardware name: Aspire one
Pid: 2596, comm: wpa_supplicant Tainted: G        W  2.6.31-10-generic #32-Ubuntu
Call Trace:
 [] warn_slowpath_common+0x6d/0xa0
 [] warn_slowpath_null+0x15/0x20
 [] ieee80211_teardown_sdata+0xda/0x1a0 [mac80211]
 [] ieee80211_if_change_type+0x4a/0xc0 [mac80211]
 [] ieee80211_change_iface+0x61/0xa0 [mac80211]
 [] cfg80211_wext_siwmode+0xc7/0x120 [cfg80211]
 [] ioctl_standard_call+0x58/0xf0

(http://www.kerneloops.org/searchweek.php?search=ieee80211_teardown_sdata)

Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

net/mac80211/cfg.c

@@ -87,6 +87,9 @@ static int ieee80211_change_iface(struct wiphy *wiphy, int ifindex,
 	if (!dev)
 		return -ENODEV;
 
+	if (netif_running(dev))
+		return -EBUSY;
+
 	if (!nl80211_type_check(type))
 		return -EINVAL;
 
@@ -96,9 +99,6 @@ static int ieee80211_change_iface(struct wiphy *wiphy, int ifindex,
 	if (ret)
 		return ret;
 
-	if (netif_running(sdata->dev))
-		return -EBUSY;
-
 	if (ieee80211_vif_is_mesh(&sdata->vif) && params->mesh_id_len)
 		ieee80211_sdata_set_mesh_id(sdata,
 					    params->mesh_id_len,