selftests: hw-net: auto-disable building the iouring C code

selftests: hw-net: auto-disable building the iouring C code

Looks like the liburing is not updated by distros very aggressively.
Presumably because a lot of packages depend on it. I just updated
to Fedora 43 and it's still on liburing 2.9. The test is 9mo old,
at this stage I think this warrants handling the build failure
more gracefully.

Detect if iouring is recent enough and if not print a warning
and exclude the C prog from build. The Python test will just
fail since the binary won't exist. But it removes the major
annoyance of having to update liburing from sources when
developing other tests.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20251121040259.3647749-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>