cfg80211: fix wext setting SSID

Pavel reported that you can't set the SSID from "foo" to
"bar". I tried reproducing, but used different values,
with different lengths, and thus never saw the obvious
problem.
Reported-by: NPavel Roskin <proski@gnu.org>
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/wireless/wext-sme.c

@@ -166,7 +166,7 @@ int cfg80211_mgd_wext_siwessid(struct net_device *dev,
 
 	if (wdev->wext.connect.ssid && len &&
 	    len == wdev->wext.connect.ssid_len &&
-	    memcmp(wdev->wext.connect.ssid, ssid, len))
+	    memcmp(wdev->wext.connect.ssid, ssid, len) == 0)
 		goto out;
 
 	if (wdev->sme_state != CFG80211_SME_IDLE) {