selftests: drv-net: give HW stats sync time extra 25% of margin

selftests: drv-net: give HW stats sync time extra 25% of margin

There are transient failures for devices which update stats
periodically, especially if it's the FW DMA'ing the stats
rather than host periodic work querying the FW. Wait 25%
longer than strictly necessary.

For devices which don't report stats-block-usecs we retain
25 msec as the default wait time (0.025sec == 20,000usec * 1.25).

Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260318033819.1469350-3-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>