net/mlx5: update translate function for sample action

net/mlx5: update translate function for sample action

Translate the attribute of sample action that include sample ratio
and sub actions list, then create the sample DR action.

The metadata register value will be lost in the default path after
Sampler in FDB due to CX5 HW limitation.

Since source vport also be shared with metadata register c0, MLX5
PMD would set the source vport to rdma-core and rdma-core will
restore the regc0 value after sampler.

Signed-off-by: Jiawei Wang <jiaweiw@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>