tcp_cubic: make the delay threshold of HyStart less sensitive

Make HyStart less sensitive to abrupt delay variations due to buffer bloat.
Signed-off-by: NSangtae Ha <sangtae.ha@gmail.com>
Acked-by: NStephen Hemminger <shemminger@vyatta.com>
Reported-by: NLucas Nussbaum <lucas.nussbaum@loria.fr>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_cubic.c

@@ -39,7 +39,7 @@
 
 /* Number of delay samples for detecting the increase of delay */
 #define HYSTART_MIN_SAMPLES	8
-#define HYSTART_DELAY_MIN	(2U<<3)
+#define HYSTART_DELAY_MIN	(4U<<3)
 #define HYSTART_DELAY_MAX	(16U<<3)
 #define HYSTART_DELAY_THRESH(x)	clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)