Updated IPSEC NAT patches for 2.6.11

Hi,

I've forward-ported Patrick McHardy's patches that make the kernel IPSEC
work with NAT.

Since there probably won't be any more big changes between 2.6.11-rc4
and the final 2.6.11 I'm posting them now.

The biggest change is in the last patch (ipsec-04-policy-checks.diff). I
needed to rewrite nf_nat_decode_session4 due to the big NAT changes. I
hope I got everything right. I couldn't find a situation where it
failed.
I also added a missing return in nat_route_key_compare that made the
kernel fail with certain compiler flags.