kernel - Change time_second to time_uptime for all expiration calculations

kernel - Change time_second to time_uptime for all expiration calculations

* Vet the entire kernel and change use cases for expiration calculations
  using time_second to use time_uptime instead.

* Protects these expiration calculations from step changes in the wall time,
  particularly needed for route table entries.

* Probably requires further variable type adjustments but the use of
  time_uptime instead if time_second is highly unlikely to ever overrun
  any demotions to int still present.