tools: ynl: add ipv4-or-v6 display hint

tools: ynl: add ipv4-or-v6 display hint

The attribute WGALLOWEDIP_A_IPADDR can contain either an IPv4
or an IPv6 address depending on WGALLOWEDIP_A_FAMILY, however
in practice it is enough to look at the attribute length.

This patch implements an ipv4-or-v6 display hint, that can
deal with this kind of attribute.

It only implements this display hint for genetlink-legacy, it
can be added to other protocol variants if needed, but we don't
want to encourage it's use.

Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250915144301.725949-12-ast@fiberby.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>