Re-enable PCAP reading in neteq_rtpplay

Reading of PCAP (Wireshark) files was not possible due to a bug in the
parsing of files. This change fixes that by adding new validator methods
to RtpFileSource that can be used to determine the input file type.

R=ivoc@webrtc.org

Review URL: https://codereview.webrtc.org/1427923003

Cr-Original-Commit-Position: refs/heads/master@{#10490}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 5eb9d578839e502e989615186b800d9d1074ea99
3 files changed