VT: Fix overflow condition in JitterCalc

[Problem] Media crashes while VT long call
[Cause] There was a miss for a condition that decides overflow.
        Previous logic decides it's overflow
        although timestamps just go through 2^31.
        By the miss, calculation of time difference
        made another overflow so media crashed.
[Solution] Disable UBSan & Simplify codes for
           the related RTP time calculations.

Bug: 198075894
Bug: 195715335

Change-Id: I1f942db9979b737e1e6b03dfa90f154b115a866f
Signed-off-by: Kim Sungyeon <sy85.kim@samsung.com>