cxgb4: add basic tc flower offload support

Add support to add/remove flows for offload.  Following match
and action are supported for offloading a flow:

Match: ether-protocol, IPv4/IPv6 addresses, L4 ports (TCP/UDP)
Action: drop, redirect to another port on the device.

The qualifying flows can have accompanying mask information.

Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>