net/mlx4_core: Add retrieval of CONFIG_DEV parameters

Add code to issue CONFIG_DEV "get" firmware command.

This command is used in order to obtain certain parameters used for
supporting various RX checksumming options and vxlan UDP port.

The GET operation is allowed for VFs too.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Shani Michaeli <shanim@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>