Add NSH proxy support for VPP renderder

Add NSH proxy support for VPP renderder

vpp 17.01 and nsh_sfc 17.01 can act as a NSH proxy,
this commit enables VPP renderer to support NSH-unaware
Service Function, in that case, users need to specify
proxy data plane locator for this SF as below:

     "sf-data-plane-locator": [
         {
             "name": "firewall-1-dpl",
             "port": 4789,
             "ip": SF2_DP_IP,
             "transport": "service-locator:vxlan",
             "service-function-forwarder": "SFF2",
             "service-function-proxy:proxy-data-plane-locator": {
                  "port": 4790,
                  "ip": SF2_PROXY_DP_IP,
                  "transport": "service-locator:vxlan-gpe"
             }
         }
     ]

SFF will send VxLAN-gpe+NSH packet to NSH proxy specified by
proxy data plane locator, NSH proxy will send VxLAN+Ethernet
to SF, NSH proxy maintains VxLAN-gpe+NSH to VxLAN+Ethernet
mapping table in order that SFF will get correct VxLAN-gpe+NSH
packets from NSH proxy.

Change-Id: If3ecc82afd6b38142b143e43f541a270f4caa470
Signed-off-by: Yi Yang <[email protected]>