osmo-pcu: Split BTS class (and struct struct gprs_rlcmac_bts) to PCU+BTS
In current code base we have a big fat global class called BTS (bts.h) which holds all global information about BTS plus BTS specific bits.
This is totally wrong, and as we extend the code we keep extending lots of accesses to this singleton BTS class making everything more messy.
We should identify which fields belong to each bts node and which belong to the entire BSS/PCU and create a new object for it (this one is the once which can be accessed through a singleton/global variable).
Then finally have bts objects in a list inside that PCU object, potentially create one for each info_ind.
Then I guess each GprsMS object needs to have a field pointing to the BTS it is attached to?