mac80211: sync dtim_count to TSF

On starting a mesh or AP BSS, the interface dtim_count
countdown should match that of the driver TSF.

Signed-off-by: Thomas Pedersen <twpedersen@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index fd1020e..f9ae9b8 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -1035,6 +1035,7 @@
 		return err;
 	}
 
+	ieee80211_recalc_dtim(local, sdata);
 	ieee80211_bss_info_change_notify(sdata, changed);
 
 	netif_carrier_on(dev);