VT: Round off TMMBR / TMMBN value to fit in RTCP

When we express number like 2162000 (0x20FD50), mantissa is 0x20FD5.
It requires 18bits to express the mantissa.
But 17bits are the limit of space on RTCP's spec. (RFC5104 4.2.1.1)
This rounding off helps for describing these cases.

Bug: 175266635

Change-Id: I3df0b7c370eb7ff3134906ebe576a8a48fea3246
Signed-off-by: Kim Sungyeon <sy85.kim@samsung.com>