vxlan: crash on configuring vxlan tunnel on l3 mode

vxlan: crash on configuring vxlan tunnel on l3 mode

Configure a vxlan tunnel using this CLI and then assign an ip address to
the vxlan tunnel cause VPP to crash immediately
create vxlan tunnel src x.x.x.x dst y.y.y.y vni 1000 decap-next node ethernet-input l3
set interface ip address vxlan_tunnel0 z.z.z.z/24

It looks like when l3 mode is configured, the code calls the wrong function
to register the interface

Type: fix
Fixes: 3e38422ab905d26ab1625c74268e30c94327ea54

Signed-off-by: Steven Luong <sluong@cisco.com>
Change-Id: Ie1a08efc028f37fb528a7dfd7048ff6836bb8ddc