vyatta-strongswan: fix for vti creation following kernel vti changes

Due to updates in the VTI module (ip_vti.c) in recent kernels, although
tunnels still appear to be created correctly, they fail to pass any
traffic.  The changes in question are to bring the vti code inline with
other changes to related ip modules, with the following commit being
the one in question.

https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git
/commit/net/ipv4/ip_vti.c?id=7263a5187f9e9de45fcb51349cf0e031142c19a1

This patch changes the way the VTIs are created, with the added benefit
that additional netfilter rules are no longer required to mark incoming
packets.

This patch also requires additional commits to the vyatta-cfg-vpn
package to take these changes into account.

Bug #358 http://bugzilla.vyos.net/show_bug.cgi?id=358