Security part needs to be checked, may fail to work.
But if it fails, it was probably not working before either.

This commit also contains adding 'static' to nr_pdcp_entity_release()
and nr_pdcp_entity_delete() (it was too complicated to do a separate
commit for this).

We also update stats in free_rx_list() (again, too complicated for
a separate commit).

openair2/RRC/NR/rrc_gNB.c probably needs some more work, it is a
bit ugly to reestablish all the drbs without checking if they
exit. It will generate warnings at runtime. I didn't do it because
I don't know the proper way.