selftests: drv-net: store addresses in dict indexed by ipver

Looks like more and more tests want to iterate over IP version,
run the same test over ipv4 and ipv6. The current naming of
members in the env class makes it a bit awkward, we have
separate members for ipv4 and ipv6 parameters.

Store the parameters inside dicts, so that tests can easily
index them with ip version.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250218225426.77726-4-kuba@kernel.org


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