vti: switch to new ip tunnel code

GRE tunnel and IPIP tunnel already switched to the new
ip tunnel code, VTI tunnel can use it too.

Cc: Pravin B Shelar <[email protected]>
Cc: Stephen Hemminger <[email protected]>
Cc: Saurabh Mohan <[email protected]>
Cc: "David S. Miller" <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Amerigo Wang