Implement move constructor for RTPFragmentationHeader.

This allows returning RTPFragmentationHeader from a method and assigning
the results to a variable.

BUG=webrtc:7760

Review-Url: https://codereview.webrtc.org/3002283002
Cr-Original-Commit-Position: refs/heads/master@{#19556}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 34960de3fb4257a2bba9847e8df3ef76dee59e77
1 file changed