/* \brief Function called by PHY to process the received RAR and check that the preamble matches what was sent by the gNB. It provides the timing advance and t-CRNTI.
@param Mod_id Index of UE instance
@param CC_id Index to a component carrier
@param frame Frame index
@param ra_rnti RA_RNTI value
@param dlsch_buffer Pointer to dlsch_buffer containing RAR PDU
@param t_crnti Pointer to PHY variable containing the T_CRNTI
@param preamble_index Preamble Index used by PHY to transmit the PRACH. This should match the received RAR to trigger the rest of
random-access procedure
@param selected_rar_buffer the output buffer for storing the selected RAR header and RAR payload
@returns timing advance or 0xffff if preamble doesn't match