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 <[e-mail]>
Reviewed-by: Donald Hunter <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/netlink/genetlink-legacy.yaml

···
                   Optional format indicator that is intended only for choosing
                   the right formatting mechanism when displaying values of this
                   type.
-                enum: [ hex, mac, fddi, ipv4, ipv6, uuid ]
+                enum: [ hex, mac, fddi, ipv4, ipv6, ipv4-or-v6, uuid ]
               struct:
                 description: Name of the nested struct type.
                 type: string

tools/net/ynl/pyynl/lib/ynl.py

···
                 formatted = hex(raw)
             else:
                 formatted = bytes.hex(raw, ' ')
-        elif display_hint in [ 'ipv4', 'ipv6' ]:
+        elif display_hint in [ 'ipv4', 'ipv6', 'ipv4-or-v6' ]:
             formatted = format(ipaddress.ip_address(raw))
         elif display_hint == 'uuid':
             formatted = str(uuid.UUID(bytes=raw))
···
         return formatted
 
     def _from_string(self, string, attr_spec):
-        if attr_spec.display_hint in ['ipv4', 'ipv6']:
+        if attr_spec.display_hint in ['ipv4', 'ipv6', 'ipv4-or-v6']:
             ip = ipaddress.ip_address(string)
             if attr_spec['type'] == 'binary':
                 raw = ip.packed