about keypair_update

[inorick]

I think the keypair_update function rotates the keys (prev <- curr <- next) if the next key pair has been acknowledged, i.e. if key_is_next in line 454 is true: https://github.com/smartalock/wireguard-lwip/blob/0c44df308984abfb9c9df628002cdf8154c55506/src/wireguard.c#L454

So the rotation looks good to me:

1. Overwrite prev with curr.
2. Overwrite curr with next.
3. Destroy next as it has been rotated to curr.