mac80211: fix IEEE80211_SDATA_DISCONNECT_RESUME

Since commit 12e7f517029dad819c45eca9ca01fdb9ba57616b,
IEEE80211_SDATA_DISCONNECT_RESUME no longer worked as
it would simply never be tested. Restore a bit of the
code removed there and in 9b7d72c1041ec5b20b24af487a9
to make it work again.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 158e6eb..44be28c 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -1267,6 +1267,7 @@
 void ieee80211_mgd_stop(struct ieee80211_sub_if_data *sdata);
 void ieee80211_mgd_conn_tx_status(struct ieee80211_sub_if_data *sdata,
 				  __le16 fc, bool acked);
+void ieee80211_sta_restart(struct ieee80211_sub_if_data *sdata);
 
 /* IBSS code */
 void ieee80211_ibss_notify_scan_completed(struct ieee80211_local *local);