sfc: Reset derived rx_bad_bytes statistic when EF10 MC is rebooted

If the MC reboots then the stats it reports to us will have been
reset.  We need to reset ours to get efx_update_diff_stat() working
properly.

(This is a re-run of commit 876be083 'sfc: Reset driver's
MAC stats after MC reboot seen'.)

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>