zebra: data structure changes for single vxlan device
This changeset introduces the data structure changes needed for
single vxlan device functionality. A new struct zebra_vxlan_vni_info
encodes the iftype and vni information for vxlan device.
The change addresses related access changes of the new data structure
fields from different files
zebra_vty is modified to take care of the vni dump information according
to the new vni data structure for vxlan devices.