psp: base PSP device support

Add a netlink family for PSP and allow drivers to register support.

The "PSP device" is its own object. This allows us to perform more
flexible reference counting / lifetime control than if PSP information
was part of net_device. In the future we should also be able
to "delegate" PSP access to software devices, such as *vlan, veth
or netkit more easily.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250917000954.859376-3-daniel.zahka@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>