Fix typo in rtp_sender.h
Fix typo in rtp_sender.h

Addendum to cl 135165, where cl upload failed without me noticing.

Bug: webrtc:8052,webrtc:8975
Change-Id: Id46f25bc4f59fc05c1ada039a2ea17a2feac75e2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/136680
Reviewed-by: Danil Chapovalov <55de8d9c2b5977da2dd48f967f21f9d606b172a5@webrtc.org>
Commit-Queue: Erik Språng <3ab8c90c99d6dd7822e0fad803ab0211dd287ae5@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#27925}

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