net: psp: add socket security association code

Add the ability to install PSP Rx and Tx crypto keys on TCP
connections. Netlink ops are provided for both operations.
Rx side combines allocating a new Rx key and installing it
on the socket. Theoretically these are separate actions,
but in practice they will always be used one after the
other. We can add distinct "alloc" and "install" ops later.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Co-developed-by: Daniel Zahka <daniel.zahka@gmail.com>
Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250917000954.859376-9-daniel.zahka@gmail.com


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