Known issues:

  - we create a neighbour entry before the first successful challenge;
  - we compute HMAC for each HMAC TLV rather than just once;
  - we only support sending one HMAC TLV;
  - we don't support key rotation.
Co-authored-by: Clara Do <clarado_perso@yahoo.fr>
Co-authored-by: Weronika Kolodziejak <weronika.kolodziejak@gmail.com>