ike-sa: Add property for interface ID

src/libcharon/sa/ike_sa.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2006-2018 Tobias Brunner
+ * Copyright (C) 2006-2019 Tobias Brunner
  * Copyright (C) 2006 Daniel Roethlisberger
  * Copyright (C) 2005-2009 Martin Willi
  * Copyright (C) 2005 Jan Hutter
@@ -1068,6 +1068,14 @@ struct ike_sa_t {
 	 */
 	void (*clear_virtual_ips) (ike_sa_t *this, bool local);
 
+	/**
+	 * Get interface ID to use as default for children of this IKE_SA.
+	 *
+	 * @param inbound		TRUE for inbound interface ID
+	 * @return				interface ID
+	 */
+	uint32_t (*get_if_id)(ike_sa_t *this, bool inbound);
+
 	/**
 	 * Create an enumerator over virtual IPs.
 	 *