The fields of KeepAliveValues should be uint (4 bytes) instead of ulong (8 bytes). See:

https://github.com/mongodb/mongo-csharp-driver/blob/v2.7.2/src/MongoDB.Driver.Core/Core/Connections/KeepAliveValues.cs#L22

The u_long types referenced here:

https://msdn.microsoft.com/en-us/library/windows/desktop/dd877220(v=vs.85).aspx

are in the C language, where u_long is 4 bytes.

The reported side effect of this bug is that hundreds of keep alive packets are sent per second.