ethdev: fix device state on detach

ethdev: fix device state on detach

The device state should be handled by the ethdev layer when possible.
Applications should not have to do it.

Not setting the state to UNUSED will make the port_id of the device
valid for all ethdev API functions, usually resulting in segfault.

Fixes: 284c908cc588 ("app/testpmd: request device removal interrupt")
Cc: stable@dpdk.org
Signed-off-by: Gaetan Rivet <gaetan.rivet@6wind.com>
Tested-by: Shachar Beiser <shacharbe@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>