quickstart: add IP neighbor for VPP

Add ARP entry to resolve MAC address for next hop,
no longer depends on traffic generator's ARP reply.

Signed-off-by: Tianyu Li <tianyu.li@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>

Change-Id: I77860bce9677a33d010a2748005fde6f49409269