This patch adds support for the use of twofish and serpent as
ESP algorithms. The ESP index numbers given are in accordance
with RFC2407, draft-ietf-ipsec-ciph-aes-cbc-00 (before Rijndael
was selected), and KAME which assigns 253 to twofishcbc.

Support for using twofish was requested on linux-kernel, and
since I noticed serpent was missing too, included that as well.