consistency of json vs human-readable UDP upstream tests

# Context

* Version of iperf3:
```
iperf 3.9 (cJSON 1.7.13)
Linux netrics 5.4.0-1042-raspi #46-Ubuntu SMP PREEMPT Fri Jul 30 00:35:40 UTC 2021 aarch64
Optional features available: CPU affinity setting, IPv6 flow label, TCP congestion algorithm setting, sendfile / zerocopy, socket pacing
```
* Hardware:
Raspberry Pi 4 8GB

* Operating system (and distribution, if any):
Ubuntu 20.04.2 LTS \n \l

# Bug Report

This is not necessarily a bug as we understand and we tried other channels like the indicated forum for questions. Our team member hasn't had approved yet so I'm trying this question here as our last resource. This measurement is part of a large funded study, so it's really important for us to get the correct understanding of this. Really appreciate your work on such an amazing tool like iperf3 and hope we're not taking too much of your time. For now, I'm cc'ing James Saxon's question here:

We have been running iperf3 3.10 on Ubuntu 20.04 raspberry pis, to test upstream UDP throughput to university servers.
We switched from recording the human-readable format to parsing the json as:
`iperf3 -c oursite.edu -p -b 1.6M -u -P 4 -t 5 -i 0 -J | jq .end.sum`
and then calculating:
`bits_per_second * (100 - lost_percent) / 100`
This very reliably yields 6.15-6.20 Mbps on my dinky home connection, whereas the human-readable version quotes 6.05-6.10 Mbps.

Am I reconstructing this correctly? If so, which one should I trust? If not, is there a way to do this?

From what I can tell, the *received* datagrams are not included in the json output (could they be added?). I seem to get the human-readable output from the calculation,

`bitrate sent * (total received - lost received ) / (total sent)`

(Again, total and lost received datagrams are only in the human-readable.)

For reference, one run with JSON and one run with human-readable are below.

Thanks for your help and for the great tool!!

Jamie Saxon

```
{
"start": 0,
"end": 5.012857,
"seconds": 5.012857,
"bytes": 4004000,
"bits_per_second": 6406234.719144246,
"jitter_ms": 2.5463201604163417,
"lost_packets": 102,
"packets": 2860,
"lost_percent": 3.5664335664335662,
"sender": true
}
```
```
Connecting to host oursite.edu, port XX
[....]
[ ID] Interval Transfer Bitrate Total Datagrams
[ 5] 0.00-5.00 sec 978 KBytes 1.60 Mbits/sec 715
[ 7] 0.00-5.00 sec 978 KBytes 1.60 Mbits/sec 715
[ 9] 0.00-5.00 sec 978 KBytes 1.60 Mbits/sec 715
[ 11] 0.00-5.00 sec 978 KBytes 1.60 Mbits/sec 715
[SUM] 0.00-5.00 sec 3.82 MBytes 6.41 Mbits/sec 2860
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams
[ 5] 0.00-5.00 sec 978 KBytes 1.60 Mbits/sec 0.000 ms 0/715 (0%) sender
[ 5] 0.00-5.03 sec 965 KBytes 1.57 Mbits/sec 2.317 ms 0/706 (0%) receiver
[ 7] 0.00-5.00 sec 978 KBytes 1.60 Mbits/sec 0.000 ms 0/715 (0%) sender
[ 7] 0.00-5.03 sec 962 KBytes 1.57 Mbits/sec 3.051 ms 3/707 (0.42%) receiver
[ 9] 0.00-5.00 sec 978 KBytes 1.60 Mbits/sec 0.000 ms 0/715 (0%) sender
[ 9] 0.00-5.03 sec 942 KBytes 1.53 Mbits/sec 2.320 ms 17/706 (2.4%) receiver
[ 11] 0.00-5.00 sec 978 KBytes 1.60 Mbits/sec 0.000 ms 0/715 (0%) sender
[ 11] 0.00-5.03 sec 852 KBytes 1.39 Mbits/sec 2.315 ms 83/706 (12%) receiver
[SUM] 0.00-5.00 sec 3.82 MBytes 6.41 Mbits/sec 0.000 ms 0/2860 (0%) sender
[SUM] 0.00-5.03 sec 3.63 MBytes 6.06 Mbits/sec 2.501 ms 103/2825 (3.6%) receiver
```
Note that this is closely related to:

https://groups.google.com/u/1/g/iperf-dev/c/dAfkp3VX0Mo/m/dMUGl7VOAwAJ
https://github.com/esnet/iperf/commit/e255a12eb9d029f6a48a9a6e55e36d7c0921ec53