net/mlx5: fix handling link status event

net/mlx5: fix handling link status event

Even though link of a port gets down, device still can receive traffic.
That is the reason why mlx5_set_link_up/down() switches rx/tx_pkt_burst().
However, if link gets down by an external command (e.g. ifconfig), it isn't
effective. It is better to change burst functions when link status change
is detected.

Fixes: 62072098b54e ("mlx5: support setting link up or down")
Cc: stable@dpdk.org
Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
Acked-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>