Philip Withnall authored Aug 12, 2014 and Olivier Crête committed Aug 21, 2014

If the socket is closed (with pseudo_tcp_socket_close()) with FIN–ACK
unsupported, it should transition to the CLOSED state when
pseudo_tcp_socket_get_next_clock() returns FALSE (as that’s the
old-style indication that the socket has closed).

This is a behaviour change from before the introduction of FIN–ACK:
previously, the socket would stay in the ESTABLISHED state. However,
this should not have been easily detectable by consumers of the API,
as pseudo_tcp_socket_is_closed() did not exist then.