Add methods for tweaking sctp cc to settingending

Relate: https://github.com/pion/sctp/pull/354

sctptransport.go

@@ -121,6 +121,9 @@ func (r *SCTPTransport) Start(capabilities SCTPCapabilities) error {
 		BlockWrite:           r.api.settingEngine.detach.DataChannels && r.api.settingEngine.dataChannelBlockWrite,
 		MaxMessageSize:       maxMessageSize,
 		MTU:                  outboundMTU,
+		MinCwnd:              r.api.settingEngine.sctp.minCwnd,
+		FastRtxWnd:           r.api.settingEngine.sctp.fastRtxWnd,
+		CwndCAStep:           r.api.settingEngine.sctp.cwndCAStep,
 	})
 	if err != nil {
 		return err

settingengine.go

@@ -84,6 +84,9 @@ type SettingEngine struct {
 		enableZeroChecksum   bool
 		rtoMax               time.Duration
 		maxMessageSize       uint32
+		minCwnd              uint32
+		fastRtxWnd           uint32
+		cwndCAStep           uint32
 	}
 	sdpMediaLevelFingerprints                 bool
 	answeringDTLSRole                         DTLSRole
@@ -525,6 +528,22 @@ func (e *SettingEngine) SetSCTPRTOMax(rtoMax time.Duration) {
 	e.sctp.rtoMax = rtoMax
 }
 
+// SetSCTPMinCwnd sets the minimum congestion window size. The congestion window
+// will not be smaller than this value during congestion control.
+func (e *SettingEngine) SetSCTPMinCwnd(minCwnd uint32) {
+	e.sctp.minCwnd = minCwnd
+}
+
+// SetSCTPFastRtxWnd sets the fast retransmission window size.
+func (e *SettingEngine) SetSCTPFastRtxWnd(fastRtxWnd uint32) {
+	e.sctp.fastRtxWnd = fastRtxWnd
+}
+
+// SetSCTPCwndCAStep sets congestion window adjustment step size during congestion avoidance.
+func (e *SettingEngine) SetSCTPCwndCAStep(cwndCAStep uint32) {
+	e.sctp.cwndCAStep = cwndCAStep
+}
+
 // SetICEBindingRequestHandler sets a callback that is fired on a STUN BindingRequest
 // This allows users to do things like
 // - Log incoming Binding Requests for debugging