iavf: handle set and get timestamps ops

Add handlers for the .ndo_hwtstamp_get and .ndo_hwtstamp_set ops which
allow userspace to request timestamp enablement for the device. This
support allows standard Linux applications to request the timestamping
desired.

As with other devices that support timestamping all packets, the driver
will upgrade any request for timestamping of a specific type of packet
to HWTSTAMP_FILTER_ALL.

The current configuration is stored, so that it can be retrieved by
calling .ndo_hwtstamp_get

The Tx timestamps are not implemented yet so calling set ops for
Tx path will end with EOPNOTSUPP error code.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Co-developed-by: Mateusz Polchlopek <mateusz.polchlopek@intel.com>
Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>