fix RTP_DUMP timestamps
fix RTP_DUMP timestamps

which was missing a setfill call, leading to invalid timestamps.

BUG=webrtc:10675

Change-Id: Ib60f9f18b250aa89103e8de70b525df13c1042bd
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/205780
Reviewed-by: Harald Alvestrand <ce816cd73d80f958d82de1df356058c2d2bca378@webrtc.org>
Commit-Queue: Philipp Hancke <563b103f57dc2044b12822c2a7559aa15cb1c987@googlemail.com>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#33183}

TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc