Configuring keys and peers

Law `config_any`: the configuration functions of noise.c and cookie.c from ANY prior state.

The other laws set devices and peers up from zeroed memory (common.h setup_device, setup_peer); this one calls
each configuration function on ANY prior contents of what it writes, in the order netlink.c / device.c / peer.c
call them when a device's private key is changed and a peer is added:
 1. wg_noise_set_static_identity_private_key(identity, ANY 32 bytes) over ANY prior identity (any public and
    private key bytes, usable or not): private = clamp(key); public = X25519(key, 9), except that an all-zero
    key leaves the public key as it was; usable exactly when the key is not all zero and X25519(key, 9) is not
    zero (common.h m_identity_of);
 2. wg_noise_precompute_static_static(P) for a peer P with ANY public key and ANY prior precomputed bytes:
    X25519(private, P's key) if the identity is usable and that is not zero, else all zero;
 3. wg_cookie_checker_precompute_device_keys over ANY prior keys: HASH("cookie--" || S_pub) and
    HASH("mac1----" || S_pub) if the identity is usable, else both all zero;
 4. wg_cookie_checker_precompute_peer_keys(P) over ANY prior keys: HASH("cookie--" || P's key), HASH("mac1----"
    || P's key);
 5. a new peer Q: wg_noise_handshake_init over ANY prior handshake contents (every field drawn, pointers
    included) with ANY public key and ANY preshared key or none: the whole handshake is the initial one (entry of
    Q, type HANDSHAKE, not hashed, no link, index 0; state ZEROED; no last consumption; the device's identity;
    the remote static key and preshared key (zero if none) as given; precomputed DH as in 2; everything else
    zero); then wg_cookie_init over ANY prior cookie state: all zero;
 6. wg_cookie_checker_init over ANY prior secret, birthdate and device: a fresh random secret (the shim's draw),
    born now, the device; its keys unchanged.
After every step: nothing else changes (the device as a whole but the fields the step writes, P as a whole -
handshake, reference count, cookie state, keypair slots, ... - but those, Q's handshake after it is set up, the
index table and ANY keypairs of P - whole objects of any content, in the table and possibly in P's slots - byte for
byte), and nothing is allocated or freed; no reference count warns.