Currently all RX frames are timestamped which results in a performance
penalty when timestamping is not needed.  The default is now being
changed to not timestamp any Rx frames (HWTSTAMP_FILTER_NONE), but
support has been added to allow changing the desired RX timestamping
mode (HWTSTAMP_FILTER_ALL -  which was the previous setting and
HWTSTAMP_FILTER_PTP_V2_EVENT are now supported) using
SIOCSHWTSTAMP. All settings were tested using the hwstamp_ctl application.
It is also noted that ptp4l, when started, preconfigures the device to
timestamp using HWTSTAMP_FILTER_PTP_V2_EVENT, so this driver continues
to work properly "out of the box".

Test setup:  x64 PC with LAN7430 ---> x64 PC as partner

iperf3 with - Timestamp all incoming packets:
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-5.05   sec   517 MBytes   859 Mbits/sec    0    sender
[  5]   0.00-5.00   sec   515 MBytes   864 Mbits/sec         receiver

iperf Done.

iperf3 with - Timestamp only PTP packets:
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-5.04   sec   563 MBytes   937 Mbits/sec    0    sender
[  5]   0.00-5.00   sec   561 MBytes   941 Mbits/sec         receiver
Signed-off-by: Vishvambar Panth S <vishvambarpanth.s@microchip.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20231020185801.25649-1-vishvambarpanth.s@microchip.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>