tcp: (fixes #2565) Documentation on NotifyNormalClose behavior

The code was fixed in 12915:fe4f8815dcad; this commit aligns documentation.

CHANGES.html

@@ -212,6 +212,8 @@ is now exported by WifiNetDevice.</li>
 </li>
   <li> The default value of the <b>EnableBeaconJitter</b> attribute in ApWifiMac was changed from false to true.
   </li>
+  <li> The NormalClose() callback of a TcpSocket object used to fire upon leaving TIME_WAIT state (2*MSL after FINs have been exchanged).  It now fires upon entering TIME_WAIT state.  Timing of the callback for the other path to state CLOSED (through LAST_ACK) has not been changed.
+  </li>
 </ul>
 
 <hr>

RELEASE_NOTES

@@ -75,6 +75,7 @@ Bugs fixed
 - Bug 2561 - TCP can not use Connect after a BindToNetDevice
 - Bug 2563 - Modify pybindgen version check to >= minimum version required
 - Bug 2564 - Simulation crashes when CtsTimeout is triggered for A-MPDU transmissions
+- Bug 2565 - TCP; do not wait for 2*MSL to notify socket close
 - Bug 2566 - BlockAckManager::GetNRetryNeededPackets missing some packets in the queue
 - Bug 2573 - Added TCP Ledbat
 - Bug 2577 - simulation crashes when A-MPDU and multiple TOS are used with RTS-CTS enabled

src/internet/doc/tcp.rst

@@ -271,9 +271,9 @@ Figure :ref:`fig-tcp-state-machine`.
   in the tx buffer has been transmitted). This does not prevent the socket in
   receiving data, and employing retransmit mechanism if losses are detected. If
   the application calls *Close()* with unread data in its rx buffer, the socket
-  will send a reset. If the socket is in the state SYN_SENT, CLOSING, LISTEN or
-  LAST_ACK, after that call the application will be notified with
-  *NotifyNormalClose()*. In all the other cases, the notification is delayed
+  will send a reset. If the socket is in the state SYN_SENT, CLOSING, LISTEN,
+  FIN_WAIT_2, or LAST_ACK, after that call the application will be notified with
+  *NotifyNormalClose()*. In other cases, the notification is delayed
   (see *NotifyNormalClose()*).
 
 -----------------------------------------
@@ -303,7 +303,7 @@ callback as well.
   - Received an ACK for the FIN sent, with or without the FIN bit set (we are in LAST_ACK)
   - The socket reaches the maximum amount of retries in retransmitting the SYN (*)
   - We receive a timeout in the LAST_ACK state
-  - After 2*Maximum Segment Lifetime seconds passed since the socket entered the TIME_WAIT state.
+  - Upon entering the TIME_WAIT state, before waiting the 2*Maximum Segment Lifetime seconds to finally deallocate the socket.
 
 *NotifyErrorClose*: *SetCloseCallbacks*, 2nd argument
   Invoked when we send an RST segment (for whatever reason) or we reached the