mlx5: Add ndo_poll_controller() implementation

This implements ndo_poll_controller in net_device_ops callbacks for mlx5,
which is necessary to use netconsole with this driver.

Acked-By: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Calvin Owens <calvinowens@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>