module-rtp-sink is sending data timestampted with clock provided from
a driver. When driver jumps (for example due ptp master change) rtp sink
has to jumps too. Rtp sink is checking for difference between expected and
actual position and is big enough the jump is done. As resync value in
driver is not equal to diff between positions, sink could ends with
not precise timestamps up to 1 quantum.
Emit discont flag when driver jumps, so sink can be reinitialized without
its own heuristic.