If the throughput is too high the JSON output parsing fails with OverflowException

[Laksen]

To reproduce just run an iperf3 server on the same machine.

Exception:

OverflowException: Value was either too large or too small for an Int32.
    at System.Convert.ThrowInt32OverflowException()
    at System.Convert.ToInt32(Int64 value)
    at Newtonsoft.Json.Linq.JToken.op_Explicit(JToken value)
    at OpenTap.Plugins.Iperf.IperfMeasurementStep.<>c.<ParseIperfOutput>b__30_1(JToken x)
    at System.Linq.Enumerable.IListSelectIterator`2.Fill(IList`1 source, Span`1 results, Func`2 func)
    at System.Linq.Enumerable.IListSelectIterator`2.ToArray()
    at OpenTap.Plugins.Iperf.IperfMeasurementStep.ParseIperfOutput(String result)