tools: ynl: add uns-admin-perm to genetlink legacy

this flag maps to GENL_UNS_ADMIN_PERM and will be used by future specs.
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20231023-send-net-next-20231023-1-v2-1-16b1f701f900@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/genetlink-legacy.yaml

@@ -337,7 +337,7 @@ properties:
               description: Command flags.
               type: array
               items:
-                enum: [ admin-perm ]
+                enum: [ admin-perm, uns-admin-perm ]
             dont-validate:
               description: Kernel attribute validation flags.
               type: array