[TCP]: Add vegas sysctl docs.

Documentation/networking/ip-sysctl.txt

@@ -307,6 +307,15 @@ tcp_westwood - BOOLEAN
 	wired networks and throughput over wireless links.   
         Default: 0
 
+tcp_vegas_cong_avoid - BOOLEAN
+	Enable TCP Vegas congestion avoidance algorithm.
+	TCP Vegas is a sender-side only change to TCP that anticipates
+	the onset of congestion by estimating the bandwidth. TCP Vegas
+	adjusts the sending rate by modifying the congestion
+	window. TCP Vegas should provide less packet loss, but it is
+	not as aggressive as TCP Reno.
+	Default:0
+
 ip_local_port_range - 2 INTEGERS
 	Defines the local port range that is used by TCP and UDP to
 	choose the local port. The first number is the first, the