Major Description
BARRIER is used by the state transfer protocols, to get the digest and the state atomically. However, the digest only keeps track of multicast (=group) messages, so we don't need to block unicast messages !
This would help us in STREAMING_STATE_TRANSFER: even though we block the BARRIER, the state chunks sent from the state provider to the state requester (when use_default_transport=true) will not get blocked with this change !
