Invoke DSCP related send methods in P2PSocketClients

R=hubbe@chromium.org
TBR=sergeyu@chromium.org
BUG=277022

Review URL: https://codereview.chromium.org/40603002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230864 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230864