Apply patch #9629: tftp_cleanup() should clean up more

By Jens Nielsen

src/apps/tftp/tftp_server.c

@@ -428,6 +428,7 @@ void tftp_cleanup(void)
 {
   LWIP_ASSERT("Cleanup called on non-initialized TFTP", tftp_state.upcb != NULL);
   udp_remove(tftp_state.upcb);
+  close_handle();
   memset(&tftp_state, 0, sizeof(tftp_state));
 }