vxlan_id_ has to be validated VnEntry::GetVxLanId()
vxlan_id_ has to be validated VnEntry::GetVxLanId()

When vxlan_routing is enabled, GetVxlan returns
vxlan_id_ without validating it. Added check to validate
it.

Change-Id: I987d7bae76310a0091ba946a337d66620692a742
Closes-bug: #1787053

eonpatapon/contrail-controller,rombie/contrail-controller,rombie/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,rombie/contrail-controller,rombie/contrail-controller