Testing of phy_stub

Necessary modifications to support noS1 with nfapi and eNB side for testing vnf-pnf up to the stage of previous commit

Testing works until the call of callback function pnf_p7_subframe_ind. There, it never satisfies the condition if(tx_subframe_buffer->sfn_sf == sfn_sf_tx) so both sides (vnf and pnf are hanging).

Connected new callback functions at nfapi_pnf for phy_stub mode + Intorducing new functions initializing UE variables and threads specific to phy_stub mode, instead of extending the existing ones + Direct connection of the timer_thread with UE_phy_stub_thread_rxn_txnp4.

Introduced a new timer_thread within lte-ue. This thread is ticking the subframes and wakes up UE_thread function which is waiting on a condition variable for nfapi_mode=3 (phy_stub)

Introduce nfapi_mode variable to differentiate functionality between phy_stub_ue mode (nfapi_mode=3) and normal full stack mode (nfapi_mode!=3).

Added functions copying nfapi requests to UE_mac_inst + Substituted calls to phy_procedures_ue rx/tx with phy_stub functions triggering MAC layer Tx/Rx procedures at UE MAC. Changes within UE_thread_rxn_txnp4

update SidelinkUEInformation (UE's side), RRCConnectionReconfiguration (eNB's side), add rrc_ue_process_radioResourceConfig to process RPs and configure MAC/PHY

Added handling of HI_DCI0_config requests at UE MAC. Eliminated calls to PHY functions from utilized UE MAC functions (e.g., ue_send_sdu) to support phy_stub operation mode.

Updated handling of DL_config and Tx_req pdus in phy_stub_UE to be compliant with nfapi callback functions

Added MAC level state variable for the UE and control mechanisms to ensure the correct operation of the UE MAC state machine.