examples/ip_pipeline: update routes when ports state change

examples/ip_pipeline: update routes when ports state change

The routing pipeline registers a callback function with the nic ports and
this function is invoked for updating the routing entries (corresponding to
local host and directly attached network) tables whenever the nic ports
change their states (up/down).

Signed-off-by: Jasvinder Singh <jasvinder.singh@intel.com>
Acked-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>