Prior to this commit, upon a release of a UE at the gNB in NSA, the gNB
fails with a segv. This is because the servingCellConfigCommon is used
in the reconfigurationWithSync (through a simple pointer). At the
release, the entire secondaryCellGroup is freed, leading to a free of
the servingCellConfigCommon. The gNB then tries to use it (e.g., for
looking up the numerology), and leading to a segv.

To avoid this problem, make a "deep copy" of the ServingCellConfigCommon
so that we can safely free the UEs secondaryCellGroup, without freeing
the initial ServingCellConfigCommon.