Enhance and fix packet trace for IP forwarding as follows:

Enhance and fix packet trace for IP forwarding as follows:
1. Add fib index to IP6 forwarding trace.
2. Display adjacency index in IP forwarding trace.
3. Fix adjacency display for L3 to L2 forwarding such as
   BVI and VXLAN tunnel decap.
4. Setup VXLAN tunnel fib index properly for packet trace.

Change-Id: I261fea5abf51e2550d24cdcee53887be2fdd08de
Signed-off-by: John Lo <loj@cisco.com>