examples/networking/misc/lwiperf: add application

[basilfx]

Contribution description

This is lwIP's built-in iPerf2 'app', provided as an example application for RIOT-OS. I came across this functionality, researching possibilities to test (to be PR'd) ethernet drivers.

I am aware of benchmark_udp. Given that the code for the built-in iPerf2 'app' is already distributed with lwIP, I think this is a nice addition to test TCP throughput, and have another utility to stress test an ethernet driver.

Testing procedure

This can be easily tested on native.

$ make -C examples/networking/misc/lwiperf
$ examples/networking/misc/lwiperf/bin/native64/lwiperf.elf tap0

On the host, start an iPerf server (-V is for IPv6):

$ iperf -V -s

Run the client on the node, connecting to the host:

> client fe80::804:9bff:feb4:23de
TCP client connecting to fe80::804:9bff:feb4:23de port 5001

The node will connect to the server and print a report afterwards:

--- Results ---
Status      : TCP client done
Remote      : FE80::804:9BFF:FEB4:23DE:5001
Transferred : 309149816 bytes
Duration    : 10000 ms
Bandwidth   : 247312 kbit/s
--------------

The host output will look as follows:

------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:  128 KByte (default)
------------------------------------------------------------
[  1] local fe80::804:9bff:feb4:23de port 5001 connected with fe80::d016:6cff:fe09:7835 port 49153
[ ID] Interval       Transfer     Bandwidth
[  1] 0.0000-9.9988 sec   295 MBytes   247 Mbits/sec

Issues/PRs references

None

Declaration of AI-Tools / LLMs usage:

AI-Tools / LLMs that were used are:

• Claude Code for the final review of the three commits

[riot-ci]

Murdock results

✔️ PASSED

b747126 fixup! examples/networking/misc/lwiperf: add application

Success	Failures	Total	Runtime
11124	0	11124	12m:35s

Artifacts

• Documentation preview

[basilfx]

Gave this another review myself:

• Guarded _session a bit more with locks.
• Documented an issue where a server on both IPv4 and IPv6 will only listen on IPv4. Not sure why, and not something I want to dig into too much. I exactly use it as documented.
• Moved dependency on lwip_tcp and lwip_arp (for IPv4) to pkg/lwip/Makefile.dep

[basilfx]

Screenshot of this application running on actual hardware (Seeeduino Arch Pro):

(don't mind the sudo thingy: has to do with macOS and local network access)