Handover support for transceiver (TCH/F TCH/H SDCCH4 SDCCH8)

It allows to enable/disable access burst detection on each subslot
individually. It should be compatible with the handover implementation
at OsmoBTS and OpenBTS.

Original authors: Dmitry Soloviev <Dmitri.Soloviev@fairwaves.ru>, Andreas Eversberg <andreas@eversberg.eu>