net/mlx5: DR, Rename action modify fields to reflect naming in HW spec

As preparation for supporting ConnectX-7, rename action modify fields
steering registers from arbitrary names to the names that reflect the
corresponding naming and location of the steering registers in HW.
These registers mapping has changed in ConnectX-7, so the renaming allows
to keep track of their mapping better.

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