> The NICs need supported hardware timestamping.

Yes. I'm aware. Perhaps I'm more stupid about this topic than normal, but it looks to me like the NICs I have do (NIC names have been changed for clarity, but all other output is untouched):

  $ ethtool -T intel-nic
  Time stamping parameters for intel-nic:
  Capabilities:
   hardware-transmit
   software-transmit
   hardware-receive
   software-receive
   software-system-clock
   hardware-raw-clock
  Hardware timestamp provider index: 0
  Hardware timestamp provider qualifier: Precise (IEEE 1588 quality)
  Hardware timestamp source: MAC
  Hardware Transmit Timestamp Modes:
   off
   on
  Hardware Receive Filter Modes:
   none
   all

  $ ethtool -T brcm-nic
  Time stamping parameters for brcm-nic:
  Capabilities:
   hardware-transmit
   software-transmit
   hardware-receive
   software-receive
   software-system-clock
   hardware-raw-clock
  Hardware timestamp provider index: 0
  Hardware timestamp provider qualifier: Precise (IEEE 1588 quality)
  Hardware timestamp source: MAC
  Hardware Transmit Timestamp Modes:
   off
   on
  Hardware Receive Filter Modes:
   none
   ptpv1-l4-event
   ptpv2-l4-event
   ptpv2-l2-event