RDMA/mlx5: Add support for flow tag to raw create flow

A user can provide a hint which will be attached to the packet and written
to the CQE on receive. This can be used as a way to offload operations
into the HW, for example parsing a packet which is a tunneled packet, and
if so, pass 0x1 as the hint. The software can use that hint to decapsulate
the packet and parse only the inner headers thus saving CPU cycles.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>