net/mlx5e: Enable CQE compression when PCI is slower than link

We turn the feature ON, only for servers with PCI BW < MAX LINK BW, as it
helps reducing PCI pressure on weak PCI slots, but it adds some software
overhead.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>