[TCP] Vegas: Increase default alpha to 2 and beta to 4.

This helps Vegas cope better with delayed ACKs, see
analysis at:

http://www.cs.caltech.edu/%7Eweixl/technical/ns2linux/known_linux/index.html#vegasSigned-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_vegas.c

@@ -42,8 +42,8 @@
  * with V_PARAM_SHIFT bits to the right of the binary point.
  */
 #define V_PARAM_SHIFT 1
-static int alpha = 1<<V_PARAM_SHIFT;
-static int beta  = 3<<V_PARAM_SHIFT;
+static int alpha = 2<<V_PARAM_SHIFT;
+static int beta  = 4<<V_PARAM_SHIFT;
 static int gamma = 1<<V_PARAM_SHIFT;
 
 module_param(alpha, int, 0644);