Introduce no-thread mode in ITTI

Introduce a --no-itti-threads command line option to disable threading
in ITTI, and call message handlers in the current thread. This is being
introduced in order to increase repeatability when testing the nrUE with
the IQPlayer. Without this feature, runs with the IQPlayer will end up
differently, depending on the timing of ITTI threads, mostly when
sending messages to RRC and NAS.

openair1/SIMULATION/NR_PHY/nr_dummy_functions.c

@@ -51,3 +51,7 @@ int8_t nr_mac_rrc_data_ind_ue(const module_id_t module_id,
                               const channel_t channel,
                               const uint8_t* pduP,
                               const sdu_size_t pdu_len) { return 0; }
+void *rrc_nrue(void *notUsed)
+{
+  return NULL;
+}