Fix Chrome datachannel stuck at closing

When close datachannel from chrome, sctp should response with an outgoingResetRequest, otherwise the chrome won't fully close the datachannel.

association.go

@@ -2023,12 +2023,41 @@ func (a *Association) resetStreamsIfAny(p *paramOutgoingResetRequest) *packet {
 		result = reconfigResultInProgress
 	}
 
-	return a.createPacket([]chunk{&chunkReconfig{
-		paramA: &paramReconfigResponse{
+	// From draft-ietf-rtcweb-data-channel-13 section-6.7:
+	//	if one side decides to close the data channel, it resets the corresponding
+	//	outgoing stream.  When the peer sees that an incoming stream was
+	//	reset, it also resets its corresponding outgoing stream.  Once this
+	//	is completed, the data channel is closed.
+
+	rsn := a.generateNextRSN()
+	tsn := a.myNextTSN - 1
+
+	c := &chunkReconfig{
+		paramA: &paramOutgoingResetRequest{
+			reconfigRequestSequenceNumber:  rsn,
 			reconfigResponseSequenceNumber: p.reconfigRequestSequenceNumber,
-			result:                         result,
+			senderLastTSN:                  tsn,
+			streamIdentifiers:              p.streamIdentifiers,
 		},
-	}})
+	}
+	a.reconfigs[rsn] = c // store in the map for retransmission
+	a.log.Debugf("[%s] sending RECONFIG : rsn=%d tsn=%d",
+		a.name, rsn, a.myNextTSN-1)
+
+	if len(a.reconfigs) > 0 {
+		a.tReconfig.start(a.rtoMgr.getRTO())
+	}
+
+	return a.createPacket([]chunk{
+		&chunkReconfig{
+			paramA: &paramReconfigResponse{
+				reconfigResponseSequenceNumber: p.reconfigRequestSequenceNumber,
+				result:                         result,
+			},
+		},
+		c,
+	})
+
 }
 
 // Move the chunk peeked with a.pendingQueue.peek() to the inflightQueue.