sctp: Move SctpTransportFactory to a separate file

Bug: webrtc:12614
Change-Id: Ifc0e96ed3262e6ca057cd73d736a7ac081493f53
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/214481
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Florent Castelli <orphis@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33663}
diff --git a/pc/connection_context.cc b/pc/connection_context.cc
index 213a8f3..4da4bb0 100644
--- a/pc/connection_context.cc
+++ b/pc/connection_context.cc
@@ -16,6 +16,7 @@
 
 #include "api/transport/field_trial_based_config.h"
 #include "media/base/rtp_data_engine.h"
+#include "media/sctp/sctp_transport_factory.h"
 #include "rtc_base/helpers.h"
 #include "rtc_base/ref_counted_object.h"
 #include "rtc_base/task_utils/to_queued_task.h"