net: devmem: ksft: add ipv4 support

ncdevmem supports both ipv4 and ipv6, but the ksft is currently
ipv6-only. Propagate the ipv4 support to the ksft, so that folks that
are limited to these networks can also test.

Signed-off-by: Mina Almasry <almasrymina@google.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250523230524.1107879-5-almasrymina@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>