fix router forwarding flag set

src/core/ipv6/nd6.c

@@ -546,7 +546,11 @@ nd6_input(struct pbuf *p, struct netif *inp)
       }
 
       /* Send back a NA for us. Allocate the reply pbuf. */
+#if ESP_LWIP && LWIP_FORCE_ROUTER_FORWARDING
+      nd6_send_na(inp, &target_address, ND6_FLAG_ROUTER | ND6_FLAG_SOLICITED | ND6_FLAG_OVERRIDE);
+#else
       nd6_send_na(inp, &target_address, ND6_FLAG_SOLICITED | ND6_FLAG_OVERRIDE);
+#endif
     }
 
     break; /* ICMP6_TYPE_NS */

src/include/lwip/opt.h

@@ -2404,6 +2404,14 @@
 #define LWIP_IPV6                       0
 #endif
 
+/**
+ * when LWIP_FORCE_ROUTER_FORWARDING is enbaled in lwip, the router flag in NA packet will always
+ * set to 1, otherwise, never set router flag for NA packets.
+ */
+#if !defined LWIP_FORCE_ROUTER_FORWARDING || defined __DOXYGEN__
+#define LWIP_FORCE_ROUTER_FORWARDING 0
+#endif
+
 /**
  * LWIP_ND6==1: Enable NDP
  * when LWIP_IPV6 is enabled in lwIP, NDP timer is enabled by default with a timeout of 1 second.