cxgb4: convert to ndo_hwtstamp API

cxgb4: convert to ndo_hwtstamp API

Convert to use .ndo_hwtstamp_get()/.ndo_hwtstamp_set() callbacks.

There is some change in the logic as well. Previously, the driver was
storing newly requested configuration regardless of whether it was
applied or not. In case of request validation error, inconsistent
configuration would be returned by the driver. New logic stores
configuration only if was properly validated and applied. It brings the
consistency between reported and actual configuration.

Signed-off-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20251016152515.3510991-6-vadim.fedorenko@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>