During the Initial UL RRC Message, the CellGroup is created. Since the
CellGroup specifies the SRB1, the SRB1 should also be created (because
the DL RRC Messages is sent via SRB1). However, before this commit, the
CellGroup is created while having the RLC lock, so we cannot create
SRB1, as it results in a deadlock.

Therefore, we now first create CellGroup, SRB0, and SRB1, before giving
the UE message to the RLC.