jool session proxy: Trigger stats server on --stats.port

Since --stats.address has a sensible default, it was weird that
--stats.port wasn't enough to kickstart the stats server.

docs/en/usr-flags-session.md

@@ -125,9 +125,9 @@ Same as `IP_MULTICAST_TTL`. From `man 7 ip`:
 #### `--stats.address`
 
 - Type: String (IPv4/v6 address)
-- Default: None (Stats server not started if absent)
+- Default: "::"
 
-Address for statistics server. It's optional; if you don't configure it, `jool session proxy` will not start it.
+Address for statistics server. It's optional; if you don't configure `--stats.address` and/or `--stats.port`, `jool session proxy` will not start the server.
 
 It's presently rudimentary, as it was spawned by a debugging session. Sample query:
 

src/usr/argp/wargp/session.c

@@ -238,8 +238,10 @@ int handle_session_proxy(char *iname, int argc, char **argv, void const *arg)
 	netcfg.out_interface = pargs.net_dev_out.value;
 	netcfg.ttl = pargs.net_ttl;
 
-	statcfg.enabled = pargs.stats_addr.value != NULL;
-	statcfg.address = pargs.stats_addr.value;
+	statcfg.enabled = pargs.stats_addr.value || pargs.stats_port.value;
+	statcfg.address = (pargs.stats_addr.value != NULL)
+			? pargs.stats_addr.value
+			: "::";
 	statcfg.port = (pargs.stats_port.value != NULL)
 			? pargs.stats_port.value
 			: "6401";
@@ -287,6 +289,27 @@ int joold_start(char const *iname, struct netsocket_cfg *netcfg,
 {
 	int error;
 
+	iname = iname ? iname : "default";
+
+	printf("Config:\n");
+	printf("  mod.instance: %s\n", iname);
+	if (netcfg->enabled) {
+		printf("  net.mcast.addr: %s\n", netcfg->mcast_addr);
+		printf("  net.mcast.port: %s\n", netcfg->mcast_port);
+		printf("  net.dev.in: %s\n", netcfg->in_interface);
+		printf("  net.dev.out: %s\n", netcfg->out_interface);
+		printf("  net.ttl: %d\n", netcfg->ttl);
+	}
+	if (statcfg->enabled) {
+		printf("  stats.addr: %s\n", statcfg->address);
+		printf("  stats.port: %s\n", statcfg->port);
+	}
+
+	printf("\n");
+	printf("joold is intended as a daemon, so it outputs straight to syslog.\n");
+	printf("The standard streams will mostly shut up from now on.\n");
+	printf("---------------------------------------------\n");
+
 	openlog("joold", 0, LOG_DAEMON);
 
 	error = modsocket_setup(iname);

src/usr/joold/joold.c

@@ -25,8 +25,6 @@ static int netsocket_config(char const *file, struct netsocket_cfg *cfg)
 	cJSON *json;
 	int error;
 
-	cfg->enabled = true;
-
 	error = read_json(file, &json);
 	if (error)
 		return error;
@@ -63,8 +61,15 @@ static void statsocket_config(char *port, struct statsocket_cfg *cfg)
 int main(int argc, char **argv)
 {
 	char *iname = "default";
-	struct netsocket_cfg netcfg = { .enabled = true, .ttl = 1 };
-	struct statsocket_cfg statcfg = { .address = "::" };
+	struct netsocket_cfg netcfg = {
+		.mcast_port = "6400",
+		.enabled = true,
+		.ttl = 1,
+	};
+	struct statsocket_cfg statcfg = {
+		.address = "::",
+		.port = "6401",
+	};
 	int error;
 
 	fprintf(stderr, "Warning: `joold` is deprecated. See `jool session proxy --help`.\n");
@@ -83,29 +88,5 @@ int main(int argc, char **argv)
 	if (argc >= 4)
 		statsocket_config(argv[3], &statcfg);
 
-	if (!netcfg.mcast_port)
-		netcfg.mcast_port = "6400";
-	if (!statcfg.port)
-		statcfg.port = "6401";
-
-	printf("Config:\n");
-	printf("  mod.instance: %s\n", iname);
-	if (netcfg.enabled) {
-		printf("  net.mcast.addr: %s\n", netcfg.mcast_addr);
-		printf("  net.mcast.port: %s\n", netcfg.mcast_port);
-		printf("  net.dev.in: %s\n", netcfg.in_interface);
-		printf("  net.dev.out: %s\n", netcfg.out_interface);
-		printf("  net.ttl: %d\n", netcfg.ttl);
-	}
-	if (statcfg.enabled) {
-		printf("  stats.addr: %s\n", statcfg.address);
-		printf("  stats.port: %s\n", statcfg.port);
-	}
-
-	printf("\n");
-	printf("joold is intended as a daemon, so it outputs straight to syslog.\n");
-	printf("The standard streams will mostly shut up from now on.\n");
-	printf("---------------------------------------------\n");
-
 	return joold_start(iname, &netcfg, &statcfg);
 }