Remove abs() use in PseudoTcp::process.
Remove abs() use in PseudoTcp::process.

Squelches a clang 3.5 compile error for using abs() with a long instead
of labs(). Updated affected code to use uint32:s to match the sign of
m_rx_srtt.

BUG=
R=fischman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/9409004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: f714e7faeaa0458394898a2b2b3de8693b767ddc

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