This part moves control channel message primitives from osmo-bts-sysmo to
common part.
In order to control ciphering fo BTS model, CIPHER (MPH_INFO) messages are
used.
The original code handled both the fact where a TIME indication would be
missed (and thus the frame number be higher than previous + 1), as well
as the two cases for combined / non-combined CCCH.
The L1SAP code removed some of those bits, which I'm re-introducing
here.
This is a regression of the code compared to the existing
sysmoBTS code, where the L1 tells us whether its AGCH or
PCH. However, it was not used even in the old code, so
we can afford to simply put a #warning here.
This first part moves BCCH message primitives from osmo-bts-sysmo to common
part. A new file "common/l1sap.c" is introduced to implement handling of
layer 1 messages from/to BTS model.