- MAC creates CellGroupConfig and sends to RRC
- the RRC does not manually update the CellGroupConfig
- MAC handles the RRC processing timer

In this commit, any updates to the CellGroupConfig previously done at
the RRC don't work. In other words, MIMO etc don't work; this is
implemented in the next commit.

Note that the change to take out spCellConfig during reestablishment is
because after reestablishment, as per spec (38.331 5.3.7.2), the UE
should drop the spCellConfig, which we generate by default on the first
UE connection.

Furthermore, add a new variable apply_cellgroup to signal if, after RRC
processing timer, we wish to apply the CellGroup. In some situations,
e.g., Msg.4 ack, we do not want to apply the CellGroup, because for
instance in reestablishment, we await for a reconfiguration of cellgroup
that would be triggered too early.