so that the call knows which packet ids were sent on the previous candidate pair. Note that packet_id is actually 16bits, so we can use -1 for values that are not set. Also moved the tests for candidate pair changes to TestSelectConnectionBeforeNomination. BUG= R=deadbeef@webrtc.org, pthatcher@webrtc.org Review URL: https://codereview.webrtc.org/1842093002 . Cr-Commit-Position: refs/heads/master@{#12184}