trap-manager: add a method to find reqid for installed traps by config

src/libcharon/sa/trap_manager.h

@@ -57,6 +57,14 @@ struct trap_manager_t {
 	 */
 	enumerator_t* (*create_enumerator)(trap_manager_t *this);
 
+	/**
+	 * Find the reqid of a child config installed as a trap.
+	 *
+	 * @param child		CHILD_SA config to get the reqid for
+	 * @return			reqid of trap, 0 if not found
+	 */
+	u_int32_t (*find_reqid)(trap_manager_t *this, child_cfg_t *child);
+
 	/**
 	 * Acquire an SA triggered by an installed trap.
 	 *