For finding the right paging group one needs to know various
settings that are broadcasted as part of system settings 3. This
includes the CCCH Conf, the BS_PA_MFRMS, BS_AG_BLKS_RES.... The
next step will be to move away from the hardcoded System Settings 3
so one can calculate the paging group...
Call use_lchan early in allocate_loc_updating_req, do not directly call
rsl_chan_release but go through channel alloc to take the use_count into
account.