ethdev: promote port ownership API as stable

ethdev: promote port ownership API as stable

The port ownership concept was introduced in ethdev in DPDK 18.02.
Not sure it is used by applications except those using failsafe or netvsc.
It can also be used by libraries or applications to sort out
how ports are controlled.

Hiding sub-ports controlled by failsafe or netvsc look to be enough
justification to promote this API as stable.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Ray Kinsella <mdr@ashroe.eu>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>