cfg80211: fix docbook

Looks like I forgot to document the "gfp" parameter
to cfg80211_gtk_rekey_notify, add it.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/net/cfg80211.h

@@ -3055,6 +3055,7 @@ void cfg80211_cqm_pktloss_notify(struct net_device *dev,
  * @dev: network device
  * @bssid: BSSID of AP (to avoid races)
  * @replay_ctr: new replay counter
+ * @gfp: allocation flags
  */
 void cfg80211_gtk_rekey_notify(struct net_device *dev, const u8 *bssid,
 			       const u8 *replay_ctr, gfp_t gfp);