net/mlx4_core: Add basic support for TCP/IP offloads under tunneling

Add the low-level device commands and definitions used for TCP/IP HW offloads
of tunneled/vxlan traffic which are supported by the ConnectX3-pro NIC.

This is done through the following elements:

 - read tunneling device caps in QUERY_DEV_CAP
 - add helper function to do SET_PORT for tunneling
 - add DMFS VXLAN steering rule definitions
 - add CQE and WQE checksum offload field definitions

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>