The core of scheduler is a simple clock counter, which relays
on system time for now. One was a bit simplified and migrated
from OsmoBTS.
Due to system time is not an ideal clock source, the counter
should be periodically corrected by clock indications from BTS.
Change-Id: I27d85bd3e2c8bca3f876f73517027b9fe43c9825
Vadim Yanitskiy