net/mlx5: Add new WQE for updating flow table

Add new WQE type: FLOW_TBL_ACCESS, which will be used for
writing modify header arguments.
This type has specific control segment and special data segment.

Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Alex Vesker <valex@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>