pay: add a dev-only parameter to deactivate shadow routing

Had to make a special pylightning function to avoid rewriting all calls
to 'pay()' with 'rpc.call()' in the next commit..

plugins/pay.c

@@ -103,6 +103,11 @@ struct pay_command {
 	/* Any remaining routehints to try. */
 	struct route_info **routehints;
 
+#if DEVELOPER
+	/* Disable the use of shadow route ? */
+	double use_shadow;
+#endif
+
 	/* Current node during shadow route calculation. */
 	const char *shadow_dest;
 };
@@ -873,6 +878,10 @@ static struct command_result *add_shadow_route(struct command *cmd,
 static struct command_result *shadow_route(struct command *cmd,
 					   struct pay_command *pc)
 {
+#if DEVELOPER
+	if (!pc->use_shadow)
+		return start_pay_attempt(cmd, pc, "Initial attempt");
+#endif
 	if (pseudorand(2) == 0)
 		return start_pay_attempt(cmd, pc, "Initial attempt");
 
@@ -1034,6 +1043,9 @@ static struct command_result *json_pay(struct command *cmd,
 	double *maxfeepercent;
 	unsigned int *maxdelay;
 	struct amount_msat *exemptfee;
+#if DEVELOPER
+	bool *use_shadow;
+#endif
 
 	if (!param(cmd, buf, params,
 		   p_req("bolt11", param_string, &b11str),
@@ -1045,6 +1057,9 @@ static struct command_result *json_pay(struct command *cmd,
 		   p_opt_def("maxdelay", param_number, &maxdelay,
 			     maxdelay_default),
 		   p_opt_def("exemptfee", param_msat, &exemptfee, AMOUNT_MSAT(5000)),
+#if DEVELOPER
+		   p_opt_def("use_shadow", param_bool, &use_shadow, true),
+#endif
 		   NULL))
 		return command_param_failed();
 
@@ -1096,6 +1111,9 @@ static struct command_result *json_pay(struct command *cmd,
 	pc->current_routehint = NULL;
 	pc->routehints = filter_routehints(pc, b11->routes);
 	pc->expensive_route = NULL;
+#if DEVELOPER
+	pc->use_shadow = *use_shadow;
+#endif
 
 	/* Get capacities of local channels (no parameters) */
 	return send_outreq(cmd, "listpeers", listpeers_done, forward_error, pc,