Before this commit, we did not read the ServingCellConfigCommon (SCC)
completely at start; rather, we read most (but not all) of it, then also
the minRXTXTIME, and at RRC initialization in
openair_rrc_gNB_configuration(), we filled the
pusch-TimeDomainAllocationList into the SCC, depending on the
minRXTXTIME.

The reason might be that we read part of the SCC, use that to fill the
NRRRC_CONFIGURATION_REQ, read also the minRXTXTIME (part of the RRC
config), and then we have all we need to "finalize the SCC". Since we
move everything to the MAC, I avoid too much upfront code changes,
hardcode the minRXTXTIME (and check with an assert), and undo this in a
later commit when the "RRC config" relevant for radio parameters, e.g.,
minRXTXTIME, is moved to MAC.

I verified the equality of the SCC before (at the end
openair_rrc_gNB_configuration()) and after (at the end of
get_scc_config()) this commit manually using a printf, assuming that
after RRC initialization, we didn't do any further modifications to the
SCC.  But in fact, I cannot know that we don't do it...