fix(sdp): update data channel to RFC format

This PR switches to generating sctp-port based SDP.
It also adds support for parsing sctp-port, but can handle
fallback to old-style sctpmap as well.
Fixes: #1778

modules/sdp/SDP.js

     elem.c('transport');
 
     // XEP-0343 DTLS/SCTP
+    const sctpport
+        = SDPUtil.findLine(this.media[mediaindex], 'a=sctp-port:', this.session);
     const sctpmap
         = SDPUtil.findLine(this.media[mediaindex], 'a=sctpmap:', this.session);
 
-    if (sctpmap) {
+    if (sctpport) {
+        const sctpAttrs = SDPUtil.parseSCTPPort(sctpport);
+
+        elem.c('sctpmap', {
+            xmlns: 'urn:xmpp:jingle:transports:dtls-sctp:1',
+            number: sctpAttrs, /* SCTP port */
+            protocol: 'webrtc-datachannel' /* protocol */
+        });
+        elem.up();
+    } else if (sctpmap) {
         const sctpAttrs = SDPUtil.parseSCTPMap(sctpmap);
 
         elem.c('sctpmap', {
         media.port = '0';
     }
     if (transport.find('>fingerprint[xmlns="urn:xmpp:jingle:apps:dtls:0"]').length) {
-        media.proto = sctp.length ? 'DTLS/SCTP' : 'UDP/TLS/RTP/SAVPF';
+        media.proto = sctp.length ? 'UDP/DTLS/SCTP' : 'UDP/TLS/RTP/SAVPF';
     } else {
         media.proto = 'UDP/TLS/RTP/SAVPF';
     }
     if (sctp.length) {
-        sdp += `m=application ${media.port} DTLS/SCTP ${
-            sctp.attr('number')}\r\n`;
-        sdp += `a=sctpmap:${sctp.attr('number')} ${sctp.attr('protocol')}`;
-
-        const streamCount = sctp.attr('streams');
-
-        if (streamCount) {
-            sdp += ` ${streamCount}\r\n`;
-        } else {
-            sdp += '\r\n';
-        }
+        sdp += `m=application ${media.port} UDP/DTLS/SCTP webrtc-datachannel\r\n`;
+        sdp += `a=sctp-port:${sctp.attr('number')}\r\n`;
+        sdp += 'a=max-message-size:262144\r\n';
     } else {
         media.fmt
             = desc

modules/sdp/SDPUtil.js

 
         return [ sctpPort, protocol, streamCount ];// SCTP port
     },
+    parseSCTPPort(line) {
+        return line.substring(12);
+    },
     buildRTPMap(el) {
         let line
             = `a=rtpmap:${el.getAttribute('id')} ${el.getAttribute('name')}/${

modules/sdp/SampleSdpStrings.js

 
 // A basic sdp application mline
 const baseDataMLineSdp = ''
-+ 'm=application 9 DTLS/SCTP 5000\r\n'
++ 'm=application 9 UDP/DTLS/SCTP webrtc-datachannel\r\n'
 + 'c=IN IP4 0.0.0.0\r\n'
 + 'b=AS:30\r\n'
 + 'a=setup:passive\r\n'
 + 'a=ice-ufrag:adPg\r\n'
 + 'a=ice-pwd:Xsr05Mq8S7CR44DAnusZE26F\r\n'
 + 'a=fingerprint:sha-256 6A:39:DE:11:24:AD:2E:4E:63:D6:69:D3:85:05:53:C7:3C:38:A4:B7:91:74:C0:91:44:FC:94:63:7F:01:AB:A9\r\n'
-+ 'a=sctpmap:5000 webrtc-datachannel 1024\r\n';
++ 'a=sctp-port:5000\r\n'
++ 'a=max-message-size:262144\r\n';
 
 // A basic sdp video mline with a single stream
 const plainVideoMLineSdp = ''
 + 'a=ssrc:116623191 cname:mT86hcsCZwQBPh6R\r\n'
 + 'a=ssrc:116623191 msid:a2548ae2-32e8-4b09-89bc-b11f3e49ac5a b3e3d760-6b1b-48bd-8519-9d6261311d28\r\n'
 + 'a=ssrc:116623191 mslabel:a2548ae2-32e8-4b09-89bc-b11f3e49ac5a\r\n'
-+ 'a=ssrc:116623191 label:b3e3d760-6b1b-48bd-8519-9d6261311d28\r\n'
-+ 'm=application 9 DTLS/SCTP 5000\r\n'
-+ 'c=IN IP4 0.0.0.0\r\n'
-+ 'b=AS:30\r\n'
-+ 'a=ice-ufrag:aLBh\r\n'
-+ 'a=ice-pwd:7IeqrWG5ryCW2X47Lso8XYdK\r\n'
-+ 'a=ice-options:trickle\r\n'
-+ 'a=fingerprint:sha-256 78:3C:F9:96:85:FB:20:25:F8:2F:AB:37:8B:8B:17:29:EF:54:7B:7C:17:2E:90:02:8A:A1:8F:A7:F9:C5:F2:90\r\n'
-+ 'a=setup:active\r\n'
-+ 'a=mid:data\r\n'
-+ 'a=sctpmap:5000 webrtc-datachannel 1024\r\n';
++ 'a=ssrc:116623191 label:b3e3d760-6b1b-48bd-8519-9d6261311d28\r\n';
 
 const recvOnlyAudioMline = ''
 + 'm=audio 54405 RTP/SAVPF 111 103 104 126\r\n'