dcsctp: Add DcSctpSocketFactory

The factory allows us to isolate the implementation from users who only
need to depend directly on the public folder now.

Bug: webrtc:12614
Change-Id: Ied09cf772ed427eaf17a7b5705f587da57405640
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/220939
Commit-Queue: Florent Castelli <orphis@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34330}
diff --git a/media/BUILD.gn b/media/BUILD.gn
index 9c57a1d..30f642a 100644
--- a/media/BUILD.gn
+++ b/media/BUILD.gn
@@ -402,9 +402,9 @@
       ":rtc_data_sctp_transport_internal",
       "../api:array_view",
       "../media:rtc_media_base",
+      "../net/dcsctp/public:factory",
       "../net/dcsctp/public:socket",
       "../net/dcsctp/public:types",
-      "../net/dcsctp/socket:dcsctp_socket",
       "../net/dcsctp/timer:task_queue_timeout",
       "../p2p:rtc_p2p",
       "../rtc_base:checks",