ttcn3-hnbgw-test crashes on TC_second_rab_assignment
Since https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/34973 was merged, osmo-hnbgw crashes during ttcn3-hnbgw-test.
This patch fixes it:
I suggest we merge this to master, and tag a new version from master (so the fix is in latest as well, and latest doesn't crash in the testsuite).
Other commits on master are about removing asserts that got hit due to wrong assumptions, increasing a timer default value and a doc fix.