PC5-U - passing (source,destination) down to PDCP/RLC/MAC (first alternative - mapping of L2Ids form IP Addresses

Works up to the reception of the RA_RESPONSE at the UE. Crashing at fill_rx_indication_UE_MAC just before sending Msg3.

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.

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

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.

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

Added remaining fill_harq indication functions + the functionality to handle ul_config request pdus arriving from nfapi-vnf: trigger the appropriate UE_MAC and fill_indication functions to prepare the UL_indications which will be put into the socket for transfer back to vnf. Main changes within phy_stub_UE().

Definition of the UE MAC interface: IF_Module_UE.h, IF_Module_UE.c, UE_MAC_interface.h and the supporting functions.

Note: this commit is work in progress. Contains initial integration of NFAPI data structures which are tested for TX path. RX path to follow.