Currently there's bts-virtual specific fields in gsm_bts which is not used
by other models and are always allocated.
An alternative would be having a union with different structs inside,
one per model, but since we already have the bts_model abstraction, in this
case it makes more sense to use that abstraction instead of filling code
with preprocessor ifdefs to guard against non-defined types, etc.
Existing model specific data is moved there.
This new infra will be user further in forthcoming commits.
Related: OS#4215
Change-Id: Ib17a752cdbaa7d5eb8c5dfa0b197f80a4f38b38e
Vadim Yanitskiy
Pau Espin
Omar Ramadan