sfc: use hardware tx timestamps for more than PTP

sfc: use hardware tx timestamps for more than PTP

The 8000 series and newer NICs all get hardware timestamps from the MAC
 and can provide timestamps on a normal TX queue, rather than via a slow
 path through the MC. As such we can use this path for any packet where a
 hardware timestamp is requested.
This also enables support for PTP over transports other than IPv4+UDP.

Signed-off-by: Bert Kenward <bkenward@solarflare.com>
Signed-off-by: Edward Cree <ecree@xilinx.com>
Link: https://lore.kernel.org/r/510652dc-54b4-0e11-657e-e37ee3ca26a9@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>