[BUG] compile failure for linux-2.6.6

[Martin Schaffner <schaffner@xxxxxx>]

Currently, netfilter relies on the headers from a previous linux 
version being installed on the system.
If I try to compile netfilter from linux-2.6.6 with only the 2.6.6 
headers installed in /usr/include,
then net/ipv4/netfilter/ipt_ECN.c doesn't compile, because it uses 
struct ipt_ECN_info,
which isn't declared anywhere in the source tree of linux-2.6.6.
The same holds for IPT_ECN_OP_* macros.

--
Martin Schaffner