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>
diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index a362523..e1731b7 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -515,6 +515,8 @@
 		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();