CFRA: mark RA complete when sending Msg2
The current contention-free random access forces a "Msg3" (which does
not exist in CFRA) to be received by a UE. Sometimes, this "Msg3" is not
received (for whatever reason), and the MAC declare that RA failed.
This is problematic, as the spec says that RA is complete once Msg2 is
received by the UE. Since the gNB cannot know when this is, simply mark
it as complete once we sent Msg2.
We still send Msg3 in CFRA, which is explained further in the commits.
Also, improve logging and stabilize an RFsim test by reducing sl_ahead.
Robert Schmidt
6fe7581eed