net/mlx5: HWS, added modify header pattern and args handling

Packet headers/metadta manipulations are split into two parts:
 - Header Modify Pattern: an object that describes which fields
   will be modified and in which way
 - Header Modify Argument: an object that provides the values
   to be used for header modification

Reviewed-by: Hamdan Agbariya <[email protected]>
Signed-off-by: Yevgeny Kliteynik <[email protected]>
Signed-off-by: Saeed Mahameed <[email protected]>

Author: kliteyn