Use rtputils.h in socket_host*.cc

Previously socket_host.cc contained the code that's used to update RTP
header in outgoing packets. It was moved to rtputils.cc in WebRTC.
This CL removes it from socket_host.cc.

BUG=547158

Review URL: https://codereview.chromium.org/1577123004

Cr-Commit-Position: refs/heads/master@{#369863}
6 files changed