Add support for Multipath TCP

src/core/link_tcp.go

@@ -27,6 +27,7 @@ func (l *links) newLinkTCP() *linkTCP {
 		_listeners: map[*Listener]context.CancelFunc{},
 	}
 	lt.listenconfig.Control = lt.tcpContext
+	setMPTCPForListener(lt.listenconfig)
 	return lt
 }
 
@@ -118,6 +119,7 @@ func (l *linkTCP) dialerFor(dst *net.TCPAddr, sintf string) (*net.Dialer, error)
 		KeepAlive: -1,
 		Control:   l.tcpContext,
 	}
+	setMPTCPForDialer(dialer)
 	if sintf != "" {
 		dialer.Control = l.getControl(sintf)
 		ief, err := net.InterfaceByName(sintf)

src/core/link_tcp_mptcp_go121.go

@@ -0,0 +1,14 @@
+//go:build go1.21
+// +build go1.21
+
+package core
+
+import "net"
+
+func setMPTCPForDialer(d *net.Dialer) {
+	d.SetMultipathTCP(true)
+}
+
+func setMPTCPForListener(lc *net.ListenConfig) {
+	lc.SetMultipathTCP(true)
+}

src/core/link_tcp_mptcp_other.go

@@ -0,0 +1,14 @@
+//go:build !go1.21
+// +build !go1.21
+
+package core
+
+import "net"
+
+func setMPTCPForDialer(d *net.Dialer) {
+	// Not supported on versions under Go 1.21
+}
+
+func setMPTCPForListener(lc *net.ListenConfig) {
+	// Not supported on versions under Go 1.21
+}

src/core/link_tls.go

@@ -30,6 +30,7 @@ func (l *links) newLinkTLS(tcp *linkTCP) *linkTLS {
 		config:     l.core.config.tls.Clone(),
 		_listeners: map[*Listener]context.CancelFunc{},
 	}
+	setMPTCPForListener(lt.listener)
 	return lt
 }