ACK incoming FIN if needed
ACK incoming FIN if needed

From RFC793:

If the FIN bit is set, signal the user "connection closing" and
return any pending RECEIVEs with same message, advance RCV.NXT
over the FIN, and send an acknowledgment for the FIN.  Note that
FIN implies PUSH for any segment text not yet delivered to the
 user.

saminiir/level-ip,saminiir/level-ip