fix(dns): Config for dynamic DNS sorting so AF_UNSPEC works in IPv6-o…

…nly network

This fix adds an option to dynamically set the order based on whether
an the host has a global (or ULA) IPv6 address, allowing a device
with both IPv4 and IPv6 enabled to work in any network configuration,
including IPv4-only, IPv6-only, and dual-stack.

components/lwip/Kconfig

@@ -1104,6 +1104,16 @@ menu "LWIP"
             help
                 This option allows you to config dns fallback server address.
 
+        config LWIP_DNS_DYNAMIC_SORT
+            bool "Dynamically sort DNS results"
+            default n
+            help
+                Dynamically sorts DNS results by available source addresses (based on RFC 6724).
+                This allows a device to return results based on the current network
+                and work across IPv4-only, IPv6-only, and dual-stack networks.
+                If this option is disabled, DNS results have a static preference for IPv4,
+                which will work in most cases but fails for some network configurations
+
     endmenu # DNS
 
     config LWIP_BRIDGEIF_MAX_PORTS

components/lwip/port/include/lwipopts.h

@@ -499,6 +499,16 @@ static inline uint32_t timeout_from_offered(uint32_t lease, uint32_t min)
 #define LWIP_DNS_SUPPORT_MDNS_QUERIES   0
 #endif
 
+/**
+ * LWIP_DNS_DYNAMIC_SORT==1: Dynamically sorts DNS results by available source addresses.
+ * This option is set via menuconfig.
+ */
+#ifdef CONFIG_LWIP_DNS_DYNAMIC_SORT
+#define LWIP_DNS_DYNAMIC_SORT   1
+#else
+#define LWIP_DNS_DYNAMIC_SORT   0
+#endif
+
 /*
    ---------------------------------
    ---------- UDP options ----------

examples/common_components/protocol_examples_common/Kconfig.projbuild

@@ -460,6 +460,16 @@ menu "Example Connection Configuration"
                 Note that the dhcpv6 client has to be started using dhcp6_enable_stateless(netif);
                 Note that the stateful address autoconfiguration is not supported.
 
+        config LWIP_DNS_DYNAMIC_SORT
+            bool "Dynamically sort DNS results"
+            default y
+            help
+                Dynamically sorts DNS results by available source addresses (based on RFC 6724).
+                This allows a device to return results based on the current network
+                and work across IPv4-only, IPv6-only, and dual-stack networks.
+                If this option is disabled, DNS results have a static preference for IPv4,
+                which will work in most cases but fails for some network configurations
+
     endif