Trigger deregistration only in SA mode
Upon press of ^C, the UE triggers a NAS deregistration. This does not work in do-ra or phy-test modes, because there is no NAS. Therefore, in non-SA modes, just stop the UE directly.
This can potentially improve the 5G RFsim CI test case, because together with a high RFsim timeout, the chances of the last HARQ status line being without retransmissions is much higher. If that does not help, we can further increase the retx threshold.