VT: Enlarge jitter buffer range from 200ms to 300ms

Some China site shows very bad N/W.
Its low bandwidth(100 ~ 150Kbps) and long average latency require this patch.

Merged-in: I32a8c55055e249e3ba3a2fce8b808a2b0b3a4f51
Change-Id: I32a8c55055e249e3ba3a2fce8b808a2b0b3a4f51
Signed-off-by: Kim Sungyeon <sy85.kim@samsung.com>