tun reader causes the seg fault after the wintun session is closed

[mary-dcouto]

we need to use the tun_kill function because the below line throws segmentation fault if we call the wintun end session after starting the tunnel. I tried to call the tun->close after uv_stop function call, still it seg faults at the same line.
uv_async_send(tun->read_available);
So until we fix the run reader issue after session close, we cannot use it.