CSHARP-3111: Set keep alive time to 120 seconds instead of 300.

Author: rstam

src/MongoDB.Driver.Core/Core/Connections/TcpStreamFactory.cs

@@ -267,7 +267,7 @@ private Socket CreateSocket(EndPoint endPoint)
                 var keepAliveValues = new KeepAliveValues
                 {
                     OnOff = 1,
-                    KeepAliveTime = 300000, // 300 seconds in milliseconds
+                    KeepAliveTime = 120000, // 120 seconds in milliseconds
                     KeepAliveInterval = 10000 // 10 seconds in milliseconds
                 };
                 socket.IOControl(IOControlCode.KeepAliveValues, keepAliveValues.ToBytes(), null);