RIOT examples/lwip_ipv4: add example for LWIP IPv4 client/server

Contribution description

This PR adds new example which shows how to implement LWIP IPv4 client and server.

Moreover, this example can be used in CI to check, if new code do not break LWIP IPv4. In the previous few months at least two problems with LWIP IPv4 are detected manually, and they should be detected by CI - see PR #21316 or PR #21342.

Testing procedure

Check client and server commands as described in the README.md.

Issues/PRs references

None

May 31 '25 16:05 krzysztof-cabaj

Murdock results

:heavy_check_mark: PASSED

e4f0c2f8efd8a9184b459e61eaca83ab4f7f18a5 examples/lwip_ipv4: enable DHCP and server autostart

Success	Failures	Total	Runtime
17	0	17	01m:47s

Artifacts

Documentation preview

Jun 03 '25 14:06 riot-ci

I try to generate makefile.ci automatically using sudo make -C ./examples/networking/misc/lwip_ipv4 generate-Makefile.ci but after around 1h and occupied 5GB of disk it still stuck at acd52832 board.

@crasbe could you add label CI: no fast fail so I could generate makefile.ci manually.

Jun 03 '25 17:06 krzysztof-cabaj

I'll run it on my work computer tomorrow, then you can address the suggestions without triggering a full rebuild on every fixup.

Jun 03 '25 19:06 crasbe

This is the result for generate-Makefile.ci for your example:

BOARD_INSUFFICIENT_MEMORY := \
    bluepill-stm32f030c8 \
    i-nucleo-lrwan1 \
    nucleo-c031c6 \
    nucleo-f030r8 \
    nucleo-f031k6 \
    nucleo-f042k6 \
    nucleo-l011k4 \
    nucleo-l031k6 \
    nucleo-l053r8 \
    samd10-xmini \
    slstk3400a \
    stk3200 \
    stm32f030f4-demo \
    stm32f0discovery \
    stm32g0316-disco \
    stm32l0538-disco \
    weact-g030f6 \
    #

Jun 04 '25 09:06 crasbe

@crasbe Thanks for Makefile.ci generation.

Jun 04 '25 16:06 krzysztof-cabaj

All remarks from review fixed. CI is green.

Jun 13 '25 10:06 krzysztof-cabaj

Can me move this PR a little forward?

Jun 18 '25 08:06 krzysztof-cabaj

Can me move this PR little forward?

Jul 08 '25 12:07 krzysztof-cabaj

@benpicco I fix most of your remarks and have questions to one or too.

Could you review the code once again and could we move this PR forward?

Aug 08 '25 07:08 krzysztof-cabaj

Beginning of new week ... good time to finish this PR :)

@benpicco - can be move it little bit forward?

Aug 18 '25 12:08 krzysztof-cabaj

@benpicco I missed your comment concerning server auto-start - and spotted it today morning.

I added server auto-start as well as DHCP configuration.

Are there any other issues which should I fix before merging this PR?

Aug 29 '25 12:08 krzysztof-cabaj