cxgb4: add geneve offload support for T6

Add geneve segmentation offload support of T6 cards.

Original work by: Santosh Rastapur <santosh@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>