Sets median values for rtt and the offset of result packets.

def _set_medians_and_extremes(self):
        """
        Sets median values for rtt and the offset of result packets.
        """

        rtts = sorted([p.rtt for p in self.packets if p.rtt is not None])
        if rtts:
            self.rtt_min = rtts[0]
            self.rtt_max = rtts[-1]
            self.rtt_median = self.calculate_median(rtts)

        offsets = sorted(
            [p.offset for p in self.packets if p.offset is not None]
        )
        if offsets:
            self.offset_min = offsets[0]
            self.offset_max = offsets[-1]
            self.offset_median = self.calculate_median(offsets)