RDMA/mlx5: Add support for drop action in DV steering

When drop action is used the matching packet will stop processing in
steering and will be dropped. This functionality will allow users to drop
matching packets.

Link: https://lore.kernel.org/r/20200504054227.271486-1-leon@kernel.org


Signed-off-by: Daria Velikovsky <daria@mellanox.com>
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>