net/mlx5e: Prevent PFC call for non ethernet ports

Port flow control supported only for ethernet ports,
therefore, prevent any call if the port type differs from
MLX5_CAP_PORT_TYPE_ETH.

Signed-off-by: Feras Daoud <ferasda@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>