bnxt_en: Add missing periodic PHC overflow check

We use the timecounter APIs for the 48-bit PHC and packet timestamps.
We must periodically update the timecounter at roughly half the
overflow interval.  The overflow interval is about 78 hours, so
update it every 19 hours (1/4 interval) for some extra margins.

Fixes: 390862f4

 ("bnxt_en: Get the full 48-bit hardware timestamp periodically")
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>