netlink: specs: rt_addr: fix the spec format / schema failures

netlink: specs: rt_addr: fix the spec format / schema failures

The spec is mis-formatted, schema validation says:

  Failed validating 'type' in schema['properties']['operations']['properties']['list']['items']['properties']['dump']['properties']['request']['properties']['value']:
    {'minimum': 0, 'type': 'integer'}

  On instance['operations']['list'][3]['dump']['request']['value']:
    '58 - ifa-family'

The ifa-family clearly wants to be part of an attribute list.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Yuyang Huang <yuyanghuang@google.com>
Fixes: 4f280376e531 ("selftests/net: Add selftest for IPv4 RTM_GETMULTICAST support")
Link: https://patch.msgid.link/20250403013706.2828322-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>