Add auto_route and auto_detect_interface for linux

common/dialer/auto_linux.go

@@ -0,0 +1,23 @@
+package dialer
+
+import (
+	"syscall"
+
+	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing/common/control"
+	E "github.com/sagernet/sing/common/exceptions"
+)
+
+func BindToInterface(router adapter.Router) control.Func {
+	return func(network, address string, conn syscall.RawConn) error {
+		interfaceName := router.DefaultInterfaceName()
+		if interfaceName == "" {
+			return nil
+		}
+		var innerErr error
+		err := conn.Control(func(fd uintptr) {
+			innerErr = syscall.BindToDevice(int(fd), interfaceName)
+		})
+		return E.Errors(innerErr, err)
+	}
+}