Try to SO_REUSEPORT on UNIX platforms

src/yggdrasil/multicast.go

@@ -1,6 +1,7 @@
 package yggdrasil
 
 import (
+	"context"
 	"fmt"
 	"net"
 	"time"
@@ -35,7 +36,10 @@ func (m *multicast) start() error {
 			return err
 		}
 		listenString := fmt.Sprintf("[::]:%v", addr.Port)
-		conn, err := net.ListenPacket("udp6", listenString)
+		lc := net.ListenConfig{
+			Control: multicastReuse,
+		}
+		conn, err := lc.ListenPacket(context.Background(), "udp6", listenString)
 		if err != nil {
 			return err
 		}

src/yggdrasil/multicast_other.go

@@ -0,0 +1,9 @@
+// +build !linux,!darwin,!netbsd,!freebsd,!openbsd,!dragonflybsd
+
+package yggdrasil
+
+import "syscall"
+
+func multicastReuse(network string, address string, c syscall.RawConn) error {
+	return nil
+}

src/yggdrasil/multicast_unix.go

@@ -0,0 +1,22 @@
+// +build linux darwin netbsd freebsd openbsd dragonflybsd
+
+package yggdrasil
+
+import "syscall"
+import "golang.org/x/sys/unix"
+
+func multicastReuse(network string, address string, c syscall.RawConn) error {
+	var control error
+	var reuseport error
+
+	control = c.Control(func(fd uintptr) {
+		reuseport = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEPORT, 1)
+	})
+
+	switch {
+	case reuseport != nil:
+		return reuseport
+	default:
+		return control
+	}
+}