mlx4: capability for link sensing

For ConnectX3 devices, we allow link sensing only if FW explicitly
reported it supports the feature.
For older versions (ConnectX1 and 2), if the card supports both link layer types
(Ethenet and Infiniband), link sensing is supported.

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>