Scheduler used for after both SYNs have been ACKed and both sides have closed the stream, but either we haven't ACKed their close or they haven't ACKed ours.

Entry conditions:

• Both sides have closed.
• At least one direction has not ACKed the close.

Events:

• Packets received (which may or may not ACK the ones sent)
• RESET received
• Message sending fails (error talking to the session)
• Message sending fails (too many resends)

Next states:

• closed - after both sending and receiving ACKs on the CLOSE
• dead - after sending or receiving a RESET