dpif-dpdk: Added debug for port and flow adds/deletes

* Added debug level logs for normal conditions
* Added error level logs for error conditions

Change-Id: I95dab09108c948231df9ceeedcd9590141e5338e
Signed-off-by: Kevin Traynor <kevin.traynor@intel.com>
Reviewed-By: Stephen Finucane <stephen.finucane@intel.com>