Add NetEqInput::PacketData::ToString method

This new method prints information about the packet.

BUG=webrtc:7467

Review-Url: https://codereview.webrtc.org/2844283002
Cr-Commit-Position: refs/heads/master@{#17922}
diff --git a/webrtc/modules/audio_coding/BUILD.gn b/webrtc/modules/audio_coding/BUILD.gn
index 4c2602b..1867d93 100644
--- a/webrtc/modules/audio_coding/BUILD.gn
+++ b/webrtc/modules/audio_coding/BUILD.gn
@@ -1111,6 +1111,7 @@
     "neteq/tools/audio_sink.h",
     "neteq/tools/encode_neteq_input.cc",
     "neteq/tools/encode_neteq_input.h",
+    "neteq/tools/neteq_input.cc",
     "neteq/tools/neteq_input.h",
     "neteq/tools/neteq_test.cc",
     "neteq/tools/neteq_test.h",