[Patch] tunnel: add a copy of include/linux/if_tunnel.h

[Cong Wang]

To clarify:

My patch is needed for kernel < 3.8, because in kernel the following
commit introduced these IFLA_IPTUN_*

commit 0974658da47cb399b76794057823bf3cd22acf37
Author: Nicolas Dichtel <nicolas.dichtel at 6wind.com>
Date:   Fri Nov 9 06:09:59 2012 +0000

    ipip: advertise tunnel param via rtnl


Please apply.

Thanks!