Use WebRTC API to convert byteorder in srtpfilter.

This CL uses WebRTC API to convert 64bit from big-endian to host-endian,
so the internal "be64_to_cpu" of libsrtp is not used. The code path of
"be64_to_cpu" in newer versions of libsrtp depends on compile-time
defines that are not available in WebRTC.

BUG=https://code.google.com/p/chromium/issues/detail?id=328475
R=juberti@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/46749004

Cr-Commit-Position: refs/heads/master@{#8904}
2 files changed