vnet: add device-input threadplacement infra

vnet: add device-input threadplacement infra

This change adds two new debug CLI command:

- "show interface placmenet" to display which
thread (main or worker) is responsible for processing
interface rx queue

vpp# show interface placement
Thread 0 (vpp_main):
  node af-packet-input:
    host-vpp1 queue 0
Thread 1 (vpp_wk_0):
  node af-packet-input:
    host-virbr0 queue 0
Thread 2 (vpp_wk_1):
  node af-packet-input:
    host-vpp2 queue 0
    host-lxcbr0 queue 0

- "set interface placmenet" to assign thread (main or worker)
which process specific interface rx queue

vpp# set interface placement host-vpp1 queue 0 main

Change-Id: Id4dd00cf2b05e10fae2125ac7cb4411b446c5e9c
Signed-off-by: Damjan Marion <damarion@cisco.com>