mac80211: fix bss_conf.dtim_period

In AP mode, the only mode where the parameter
is supposed to be valid, we never assign it!
Fix that to allow drivers to avoid parsing
the TIM IE for the value.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/cfg.c

@@ -515,6 +515,8 @@ static int ieee80211_config_beacon(struct ieee80211_sub_if_data *sdata,
 		if (old)
 			memcpy(new->tail, old->tail, new_tail_len);
 
+	sdata->vif.bss_conf.dtim_period = new->dtim_period;
+
 	rcu_assign_pointer(sdata->u.ap.beacon, new);
 
 	synchronize_rcu();