mac80211: Fix power save in change interface

we found that power save is not getting enabled when we do
change interface in this order STA->IBSS->STA. this is
because ieee80211_setup_sdata clears type-dependent union

Reported-by: Leela Kella <leela@qca.qualcomm.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/mlme.c

@@ -2371,6 +2371,7 @@ void ieee80211_sta_setup_sdata(struct ieee80211_sub_if_data *sdata)
 		    (unsigned long) sdata);
 
 	ifmgd->flags = 0;
+	ifmgd->powersave = sdata->wdev.ps;
 
 	mutex_init(&ifmgd->mtx);