Comment 2 for bug 1785816

We don't have any reason noted for having that option disabled. But based on the kconfig help text I'd guess that it's because it adds overhead to all network activity:

   This allows timestamping of network packets by PHYs with
   hardware timestamping capabilities. This option adds some
   overhead in the transmit and receive paths.

We need to do some testing to try and quantify this overhead.