Correctly calculates the slot for multiple TDD periods.

The OAI-UE needs to have PUCCH scheduled at least six slots in advance.
Since we do not support this (yet), but assume that two slots are
enough, we schedule the UE only in slot 1 so it has 6 slots until slot 7
to send PUCCH.

Cf. commits 5c62091b and 9a503d98

- To check the current slot is the scheduled slot(UL slot - K2) and
  only execute the post processor in scheduled slot.