[inetstack] Lost packet on close

[iyzhang]

Description

If there are packets in the send queue or retransmission queue when the application closes the socket, they will be lost because the background coroutine will immediately exit. This might be happening more frequently after we moved all of our packets to go through the send queue.

How to Reproduce

Steps to reproduce the behavior:

1. Send packets to fill the window
2. Buffered packets waiting to be sent out.
3. Close the socket
4. The last packet is never sent.

Expected Behavior

Any data pushed before the close call should be eventually sent to the destination. If packets are lost, they should be retransmitted. No packets should be lost because TCP must be reliable. The socket should not be totally closed until all data is sent.