Reland of: Separating SCTP code from BaseChannel/MediaChannel.

The BaseChannel code is geared around RTP; the presence of media engines,
send and receive streams, SRTP, SDP directional attribute negotiation, etc.
It doesn't make sense to use it for SCTP as well. This separation should make
future work both on BaseChannel and the SCTP code paths easier.

SctpDataEngine now becomes SctpTransport, and is used by WebRtcSession
directly. cricket::DataChannel is also renamed, to RtpDataChannel, so it
doesn't get confused with webrtc::DataChannel any more.

Beyond just moving code around, some consequences of this CL:
- We'll now stop using the worker thread for SCTP. Packets will be
  processed right on the network thread instead.
- The SDP directional attribute is ignored, as it's supposed to be.

BUG=None

Review-Url: https://codereview.webrtc.org/2564333002
Review-Url: https://codereview.webrtc.org/2564333002
Cr-Original-Commit-Position: refs/heads/master@{#15973}
Committed: https://chromium.googlesource.com/external/webrtc/+/67b3bbe639645ab719972682359acda303d94454
Cr-Original-Original-Commit-Position: refs/heads/master@{#15906}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 953c2cea5ef35e2278a512dfd466c47cca2203a6
diff --git a/api/webrtcsdp.cc b/api/webrtcsdp.cc
index e5ee416..2c1ba64 100644
--- a/api/webrtcsdp.cc
+++ b/api/webrtcsdp.cc
@@ -33,7 +33,7 @@
 #include "webrtc/media/base/cryptoparams.h"
 #include "webrtc/media/base/mediaconstants.h"
 #include "webrtc/media/base/rtputils.h"
-#include "webrtc/media/sctp/sctpdataengine.h"
+#include "webrtc/media/sctp/sctptransportinternal.h"
 #include "webrtc/p2p/base/candidate.h"
 #include "webrtc/p2p/base/p2pconstants.h"
 #include "webrtc/p2p/base/port.h"