ethdev: fix representor port ID search by name

ethdev: fix representor port ID search by name

The patch is required for all PMDs which do not provide representors
info on the representor itself.

The function, rte_eth_representor_id_get(), is used in
eth_representor_cmp() which is required in ethdev class iterator to
search ethdev port ID by name (representor case). Before the patch
the function is called on the representor itself and tries to get
representors info to match.

Search of port ID by name is used after hotplug to find out port ID
of the just plugged device.

Getting a list of representors from a representor does not make sense.
Instead, a backer device should be used.

To this end, extend the rte_eth_dev_data structure to include the port ID
of the backing device for representors.

Signed-off-by: Viacheslav Galaktionov <viacheslav.galaktionov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Acked-by: Haiyue Wang <haiyue.wang@intel.com>
Acked-by: Beilei Xing <beilei.xing@intel.com>
Reviewed-by: Xueming Li <xuemingl@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>