ethdev: fix port id allocation

ethdev: fix port id allocation

rte_eth_dev_find_free_port() found a free port by state checking.
The state field are in local process memory, so other DPDK processes
may get the same port ID because their local states may be different.

Replace the state checking by the ethdev port name checking,
so, if the name is an empty string the port ID will be detected as
unused.

Fixes: d948f596fee2 ("ethdev: fix port data mismatched in multiple process model")
Cc: stable@dpdk.org
Suggested-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Signed-off-by: Matan Azrad <matan@mellanox.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>