doc: Tighten-up and clarify description of tcp_fin_timeout

The description for tcp_fin_timeout should be tigher and more clear.

In addition to being tighter, we should make the spelling of the
state name consistent with what utilities report, remove the now
dated reference to 2.2 and put the default in the consistent place.

Signed-off-by: Rick Jones <rick.jones2@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -224,15 +224,14 @@ tcp_fack - BOOLEAN
 	The value is not used, if tcp_sack is not enabled.
 
 tcp_fin_timeout - INTEGER
-	Time to hold socket in state FIN-WAIT-2, if it was closed
+	The length of time an orphaned (no longer referenced by any
-	by our side. Peer can be broken and never close its side,
+	application) connection will remain in the FIN_WAIT_2 state
-	or even died unexpectedly. Default value is 60sec.
+	before it is aborted at the local end.  While a perfectly
-	Usual value used in 2.2 was 180 seconds, you may restore
+	valid "receive only" state for an un-orphaned connection, an
-	it, but remember that if your machine is even underloaded WEB server,
+	orphaned connection in FIN_WAIT_2 state could otherwise wait
-	you risk to overflow memory with kilotons of dead sockets,
+	forever for the remote to close its end of the connection.
-	FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1,
+	Cf. tcp_max_orphans
-	because they eat maximum 1.5K of memory, but they tend
+	Default: 60 seconds
-	to live longer.	Cf. tcp_max_orphans.
 
 tcp_frto - INTEGER
 	Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.