net/virtio: fix link update in speed feature

net/virtio: fix link update in speed feature

Link update callback reports speed/duplex based on data
filled on device initialization. This is wrong in case of
VIRTIO_NET_F_SPEED_DUPLEX is negotiated since link could
be down at this time. Fix this function to actually
update the HW data in this case with respect to the fact
that specifying speed via devarg is a highest priority.

Fixes: 1357b4b36246 ("net/virtio: support Virtio link speed feature")
Cc: stable@dpdk.org
Signed-off-by: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>