Paging refers to a BTS. To page a mobile phone, the current location is
required. If paging succeeds or expires, the BTS structure is also given
to the callback function (cbfn).
Because paging refers to a BTS, the cbfn (callback function) must
include a pointer to bts.
There is no implementation yet for the paging of the actual BTS where
the subscriber is located. gsm_04_08.c always uses BTS 0 (in later
patches) The database requires improvement to store the current BTS
number.