sys/net/netutils: add netutils_get_ipv4()

[HendrikVE]

Contribution description

Add function netutils_get_ipv4() to netutils.

Testing procedure

Existing test in tests/netutils was extended.

Can be tested with #17763

[miri64]

After #16688 was merged I tried to port the examples to used URIs (utilizing the uri_parser) module, which was halted, since netutils_get_ipv6() requires a string (\0 terminated char array) and not a char buffer (a char array + length), the latter being the output of the non-destructive uri_parser. Maybe in the design of netutils_get_ipv4() this lack in the original netutils_get_ipv6() can already be addressed?

[HendrikVE]

After #16688 was merged I tried to port the examples to used URIs (utilizing the uri_parser) module, which was halted, since netutils_get_ipv6() requires a string (\0 terminated char array) and not a char buffer (a char array + length), the latter being the output of the non-destructive uri_parser. Maybe in the design of netutils_get_ipv4() this lack in the original netutils_get_ipv6() can already be addressed?

Unfortunately it can't, because the root of the problem is that sock_dns_query, which is used by netutils_get_ipv4 and netutils_get_ipv6, requires a null-terminated string .

[miri64]

Unfortunately it can't, because the root of the problem is that sock_dns_query, which is used by netutils_get_ipv4 and netutils_get_ipv6, requires a null-terminated string .

That sounds also like a fixable problem ;-), but I can understand if you are not willing to do it here. :-)

[HendrikVE]

Yeah I think that's something for another PR, but I can add it to my list ;)

[benpicco]

Looks good to me. Let's not go down a rabbit hole for adding some simple functionality.
Just some small nitpicks: