mac80211: make ieee80211_assign_beacon() static

This function is not used anywhere else than in cfg.c, so there's no
need to export it.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/ieee80211_i.h

@@ -1461,8 +1461,6 @@ void ieee80211_del_virtual_monitor(struct ieee80211_local *local);
 
 bool __ieee80211_recalc_txpower(struct ieee80211_sub_if_data *sdata);
 void ieee80211_recalc_txpower(struct ieee80211_sub_if_data *sdata);
-int ieee80211_assign_beacon(struct ieee80211_sub_if_data *sdata,
-			    struct cfg80211_beacon_data *params);
 
 static inline bool ieee80211_sdata_running(struct ieee80211_sub_if_data *sdata)
 {