add UE Context Setup Req at CU/DU

- add message sender (CU) + handler (CU) and fill with data from ITTI message
- add PLMNID_TO_MCC_MNC and BIT_STRING_TO_TRANSPORT_LAYER_ADDRESS_IPv4 macros
- correct TRANSPORT_LAYER_ADDRESS_TO_BIT_STRING:
  change name to TRANSPORT_LAYER_ADDRESS_IPv4_TO_BIT_STRING, make it send 4B, not 5