netdev-dpdk: Refactor vhost custom stats for extensibility.
vHost interfaces currently has only one custom statistic, but there
might be others in the near future. This refactoring makes the code
work in the same way as it done for dpdk and afxdp stats to keep the
common style over the different code places and makes it easily
extensible for the new stats addition.
Signed-off-by: Ilya Maximets <i.maximets@samsung.com> Reviewed-by: David Marchand <david.marchand@redhat.com> Acked-by: Kevin Traynor <ktraynor@redhat.com>