cxgb4: add tc flower match support for tunnel VNI

Adds support for matching flows based on tunnel VNI value.
Introduces fw APIs for allocating/removing MPS entries related
to encapsulation. And uses the same while adding/deleting filters
for offloading flows based on tunnel VNI match.

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