Keyed IPv6 tunnel

Hi
Here is implementation of simple keyed ipv6 tunnel draft:
http://tools.ietf.org/html/draft-mkonstan-keyed-ipv6-tunnel-01

Main idea is to prepare header template and prepend it to every encapsulated packet, with correct payload length, of course. It makes encapsulation path very cheap.

On decapsulation path I match next header, cookie and local/remore addresses and then remove tunnel header for conformant packets.