net/mlx5: fix link speed info when link is down

net/mlx5: fix link speed info when link is down

When the link is down, the link speed returned by ethtool is
UINT32_MAX and the link status is 0.

In this case, the DPDK ethdev link speed should be set to
ETH_SPEED_NUM_NONE.
Otherwise since link speed is non-zero but link status is zero, this
is an inconsistent situation and -EAGAIN is returned, which is not right.

Fixes: 188408719888 ("net/mlx5: fix support for newer link speeds")
Cc: stable@dpdk.org
Signed-off-by: Xiaoyu Min <jackmin@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>