default interface selected when gateway is valid (#54)

* default_route: only if not already set to elsewhere
* interface set as default when gw is valid
* +deregister default interface

glue-lwip/lwip-git.c

@@ -312,19 +312,21 @@ void esp2glue_netif_set_default (int netif_idx)
 static void netif_sta_status_callback (struct netif* netif)
 {
 	// address can be set or reset/any (=0)
+	// netif is netif_sta
 
 	uprint(DBG "netif status callback:\n");
 	new_display_netif(netif);
 
 	// tell ESP that link is updated
 	glue2esp_ifupdown(netif->num, ip_2_ip4(&netif->ip_addr)->addr, ip_2_ip4(&netif->netmask)->addr, ip_2_ip4(&netif->gw)->addr);
 
-	if (   netif->flags & NETIF_FLAG_UP
-	    && netif == netif_sta)
+	if (netif->flags & NETIF_FLAG_UP)
 	{
-		// this is our default route
-		netif_set_default(netif);
-
+		if ((netif_default == NULL) && !ip_addr_isany(&netif->gw)) {
+			// STA interface can be our default route if there is currently none and if there is a valid gw address
+			netif_set_default(netif);
+		}
+
 		// If we have a valid address of any type restart SNTP
 		bool valid_address = ip_2_ip4(&netif->ip_addr)->addr;
 
@@ -340,6 +342,11 @@ static void netif_sta_status_callback (struct netif* netif)
 			sntp_init();
 		}
 	}
+	else
+	{
+	    if (netif_default == netif)
+	        netif_set_default(NULL);
+	}
 }
 
 static void netif_init_common (struct netif* netif)