Reland "Add QWAVE/DSCP support for unconnected sockets.  Create a helper class for maintaining remote addresses that have been configured for dscp.  Adapted from cl 682456."

This is a reland of 86cf2b472f51547ab2ded2a843740bddc70ad15c

Original change's description:
> Add QWAVE/DSCP support for unconnected sockets.  Create a helper class for maintaining remote addresses that have been configured for dscp.  Adapted from cl 682456.
> 
> Bug: webrtc:5836
> Change-Id: I2ded915e82a7e967962ff3b1f4027b422d055157
> Reviewed-on: https://chromium-review.googlesource.com/1191925
> Commit-Queue: Tim Haloun <thaloun@chromium.org>
> Reviewed-by: Ryan Hamilton <rch@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#594931}

Bug: webrtc:5836
Change-Id: I77d7bde804e9d0b906da659865b058456419390a
Reviewed-on: https://chromium-review.googlesource.com/c/1252913
Commit-Queue: Tim Haloun <thaloun@chromium.org>
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597711}
3 files changed