don't fail in library utility function, return with error code instead and let
application decide what is best on how to proceed

* check whether a library has been loaded before; in this case, don't allocate
  new memory but load from old library again
* vital parameters, previous exit_fun are checked by AssertFatal()
* structure has changed a bit to make it easier to follow (instead of nested
  ifs includes one goto to the end of the function)
* formatting has been improved

* put mutex lock around instance_prach
* destroy attributes

* instead of the lengthy YAML parsing, can now handle protobuf message
* after setting the parameters, send a message to ENB_APP to perform it
* old YAML way still works

* join pthread_FH (ru_thread) once all condition variables have been set
* join RU FHTX only if it has been started (check as for pthread_create())
* join PRACH thread in the monolithic case
* send broadcast on condition variable cond_eNBs, as there can be multiple
  waits on it
* integrate stop_ru(*ru) into kill_RU_proc(*ru)
* Correct memory freeing

* init_td_thread()/init_te_thread() are only initialized depending on condition
  get_nprocs() > 2 && codingw
* apply the same the same for the functions kill_td_thread()/kill_te_thread()

* properly allocate memory for scheduler name/sorting
* free mem of sc_update, include todo for slice_config
* set has_x to one, add fct whether sorting update necessary
* set n_ul/n_dl to correct value after every loop iteration
* support for delete of multiple slices
* allocate memory for scheduler name in slice_config
* check that we really set the scheduler

- in order to facilitate the steps as verification and parameter setting,
  slices are "filled up" with default values:
  * if it is an update, with the values of the concerned slice
  * if it is a new one, with the parameters of slice 0
- because of this, it can be assumed that all slices have all parameters

- whether a scheduler callback has to be changed is now handled by the agent

- setter & getter have been renamed
- setter sets scheduler name and links to the corresponding function
- it also returns whether it succeeded (whether the scheduler callback is
  non-null)
- it performs a strdup on the scheduler name
- the remove function free the scheduler function name

- until now, on every iteration, the scheduler checked for changed parameter
  (and verified some)
- this functionality moves to the FlexRAN Agent, which verifies all parameters
  * individually, e.g. Max MCS <= 28 for DL
  * group-based, e.g. the sum of slice percentages is <= 100
- slice configuration changes are only applied if all verifications pass
- it is assumed in the scheduler, that configuration passed from outside is
  correct and can be used "as-is"

fix accounting setting

- uncomment "Couldn't find RNTI for UE X" in UE_RNTI() and rb_alloc in
  pre_processor_reset() as they only inflate the debug output with little
  benefited
- "doing ue_schedule_spec" is now displayed for individual UEs (and individual
  CCs)
- show messages when not scheduling UE in ue_schedule_spec() due to invalid
  slice or if not in RRC_CONNECTED

- 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