Add bts counters to count BTS events where we don't have a bts

In some (error-) cases we might be unable to determine which BTS to use
when counting handover events. We don't want to loose these events
because then ctr(bsc) == sum(ctr(bsc->bts)) would not be true anymore.

Those events are now counted by a counter in struct gsm_network which
uses an index that is out of range for regular BTS (65536).

Change-Id: Ic0f3edd5dc014c4eac5e8423133633a3e5d4c13e
Related: SYS#4877
4 files changed