- slice multiplexing resorts UE_list for its purposes with restoring the
  original order
- in order to keep the order in UE_list, resort to original order after
  multiplexing
- ideally, this would happen in the multiplexing but currently, the slice_idx
  is not passed to multiplexing (it does not care), so this cannot be done ATM

Prevent sc_update from being changed by an incoming slice reconfiguration
change while writing data to the scheduler

- flexran_agent_ue_config_reply() and flexran_agent_ue_state_change() send
  slice_id

Incoming slice configuration changes are buffered in an intermediate structure.
The MAC scheduler periodically polls the agent about changes. If there has been
a slice configuration change, apply it.

adds support for:
* create/remove slices
* change UE-slice association
* read/write slice parameters
* find slice index via ID

slice_counter had a wrong condition, not scheduling in DLSCH if the number of
slices is greater than one

- introduce structure in RC for slicing conf (UL/DL)
- move global variables regarding slice configuration into RC
- change ue_slice_membership(): consider UL/DL
- remove the unnecessary header files
- set default parameters: one slice

Bug only occurs when compiling without AVX2

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>