dcsctp: start SCTP_DUMP on a new line

for consistency with usrsctp_dumppacket which prefixes its output with a newline.
This makes the packets easier to grep and process with text2pcap.

BUG=webrtc:12614

Change-Id: I67bc2e0026250b21b030daf967ebc697640f2d7e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/220102
Reviewed-by: Victor Boivie <boivie@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@nvidia.com>
Cr-Commit-Position: refs/heads/master@{#34114}

media/sctp/dcsctp_transport.cc

@@ -98,7 +98,7 @@ class TextPcapPacketObserver : public dcsctp::PacketObserver {
                    dcsctp::TimeMs now,
                    rtc::ArrayView<const uint8_t> payload) {
     rtc::StringBuilder s;
-    s << prefix;
+    s << "\n" << prefix;
     int64_t remaining = *now % (24 * 60 * 60 * 1000);
     int hours = remaining / (60 * 60 * 1000);
     remaining = remaining % (60 * 60 * 1000);