Define a special XFRM mark_t.value that dynamically uses the CHILD_SA reqid

src/libhydra/kernel/kernel_ipsec.h

@@ -171,6 +171,11 @@ struct mark_t {
 	u_int32_t mask;
 };
 
+/**
+ * Special mark value that uses the reqid of the CHILD_SA as mark
+ */
+#define MARK_REQID (0xFFFFFFFF)
+
 /**
  * Interface to the ipsec subsystem of the kernel.
  *