Flush STA entries in hostapd when clearing STAs from kernel

This is needed to keep kernel and hostapd in sync. In addition,
the obsolete entry in hostapd prevented use of Deauthentication
or Disassociation frame with reason code 6/7 mechanism to indicate
to the STA that there is no association if the STA missed the
broadcast Deauthentication frame for any reason.

src/ap/hostapd.c

@@ -341,6 +341,7 @@ static int hostapd_flush_old_stations(struct hostapd_data *hapd)
 	wpa_printf(MSG_DEBUG, "Deauthenticate all stations");
 	os_memset(addr, 0xff, ETH_ALEN);
 	hostapd_drv_sta_deauth(hapd, addr, WLAN_REASON_PREV_AUTH_NOT_VALID);
+	hostapd_free_stas(hapd);
 
 	return ret;
 }