Allow MACs and not only HMACs

[tuexen]

So an authentication algorithm for SCTP-AUTH should not be required to use HMAC. It appears better to have the algorithms define themselves if they are using HMAC or might be using some other way of deriving the authentication tag. This will require that the algorithms also define a KDF of the input key data if not using HMAC. As in many cases the input shared association key will be longer than the what the algorithm uses.

This was reported in Comments on draft-tuexen-tsvwg-rfc4895-bis-04.