mlxsw: Send PTP packets as data packets to overcome a limitation

In Spectrum-2 and Spectrum-3, the correction field of PTP packets which are
sent as control packets is not updated at egress port. To overcome this
limitation, PTP packets which require time stamp, should be sent as data
packets with the following details:
1. FID valid = 1
2. FID value above the maximum FID
3. rx_router_port = 1

>From Spectrum-4 and on, this limitation will be solved.

Extend the function which handles TX header, in case that the packet is
a PTP packet, add TX header with type=data and all the above mentioned
requirements. Add operation as part of 'struct mlxsw_sp_ptp_ops', to be
able to separate the handling of PTP packets between different ASICs. Use
the data packet solution only for Spectrum-2 and Spectrum-3. Therefore, add
a dedicated operation structure for Spectrum-4, as it will be same to
Spectrum-2 in PTP implementation, just will not have the limitation of
control packets.

Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>