- New get_custom_stats interface function is added to netdev. It
  allows particular netdev implementation to expose custom
  counters in dictionary format (counter name/counter value).
- New statistics are retrieved using experimenter code and
  are printed as a result to ofctl dump-ports.
- New counters are available for OpenFlow 1.4+.
- New statistics are printed to output via ofctl only if those
  are present in reply message.
- New statistics definition is added to include/openflow/intel-ext.h.
- Custom statistics are implemented only for dpdk-physical
  port type.
- DPDK-physical implementation uses xstats to collect statistics.
  Only dropped and error counters are exposed.

Co-authored-by: Ben Pfaff <blp@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Signed-off-by: Michal Weglicki <michalx.weglicki@intel.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>