wireless: correct sparse warning in wext-compat.c

  CHECK   net/wireless/wext-compat.c
net/wireless/wext-compat.c:1434:5: warning: symbol 'cfg80211_wext_siwpmksa' was not declared. Should it be static?

Add declaration in cfg80211.h.  Also add an EXPORT_SYMBOL_GPL, since all
the peer functions have it.

Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 9b8b3f4..f68ae54 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -1963,6 +1963,10 @@
 			struct iw_request_info *info,
 			struct sockaddr *ap_addr, char *extra);
 
+int cfg80211_wext_siwpmksa(struct net_device *dev,
+			   struct iw_request_info *info,
+			   struct iw_point *data, char *extra);
+
 /*
  * callbacks for asynchronous cfg80211 methods, notification
  * functions and BSS handling helpers