This commit enables more slots so that the "real UE" preprocessor can
schedule them. The DL phytest preprocessor continues to only schedule
slots 1 & 3.  This is because 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 & 3
so it has 6 slots until slot 7 to send PUCCH.

made L1 DLSCH encoding stateless. harq_pid/round information are not kept in PHY. Full channel encoding is performed for each transmission of a transport block.
Still to be done: test, then cleanup data structures and fix unitary simulations.

mac_remove_nr_ue(): no need to memset sched_ctrl, since it is done on
connection of a UE

the whole UE_sched_ctrl is initialized in add_new_nr_ue(), which will
also init the per-UE HARQ.

Before this commit, the DLSCH scheduler would construct the MAC PDU by
reading RLC data into a memory on the stack, and then construct the PDU
with CEs first. There are at least two problems:
- we need to keep track of the exact number of bytes of CEs (cumbersome)
  to calculate the number of MAC SDUs to include
- we needlessly copy data around.

This commit does the following instead:
- write all CEs first (no need of keeping track of this in DLSCH and a
  separate function)
- then read MAC SDUs directly into nFAPI as much as possible or
  necessary, without recopying