modifications for SRB0 to allow multiple UE contexts in case of delayed CCCH reception in CU/DU split (moved SRB0 from carrier to UE context)

removed assertion in MAC layer and adjusted generation of MSG4 to handle when CCCH message is not present. UL CCCH is now received in CU, but asserts. Need to add code in DU to handle scheduling of DL-CCCH in later subframe. In current state, DL-CCCH will only come out if it is ready for MSG$ transmission.

Merge branch 'feature-127-protocol-split' of https://gitlab.eurecom.fr/oai/openairinterface5g into feature-127-protocol-split

Conflicts:
	openair2/F1AP/f1ap_cu_interface_management.c
	openair2/F1AP/f1ap_du_interface_management.c

Merge branch 'feature-127-protocol-split' of https://gitlab.eurecom.fr/oai/openairinterface5g into feature-127-protocol-split

Merge branch 'feature-127-protocol-split' of https://gitlab.eurecom.fr/oai/openairinterface5g into feature-127-protocol-split

Merge branch 'feature-127-protocol-split' of https://gitlab.eurecom.fr/oai/openairinterface5g into feature-127-protocol-split

Merge branch 'feature-127-protocol-split' of https://gitlab.eurecom.fr/oai/openairinterface5g into feature-127-protocol-split

note: doesn't compile yet.

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>