fix(dns): Fix a bug of the seq number is overflow, if we don't have f…

…ound an unused entry and table is full, use the oldest completed one.

third_party/lwip/core/dns.c

@@ -896,6 +896,17 @@ dns_enqueue(const char *name, dns_found_callback found, void *callback_arg)
       if ((dns_seqno - pEntry->seqno) > lseq) {
         lseq = dns_seqno - pEntry->seqno;
         lseqi = i;
+      } else {
+        if (pEntry->seqno >= (0xFF - DNS_TABLE_SIZE)) {
+          static u8 index = 0;
+          if ((pEntry->seqno - (0xFF - DNS_TABLE_SIZE)) == index) {
+            index ++;
+            lseqi = i;
+            if (index == DNS_TABLE_SIZE) {
+              index = 0;
+            }
+          }
+        }
       }
     }
   }
@@ -918,13 +929,17 @@ dns_enqueue(const char *name, dns_found_callback found, void *callback_arg)
 
   /* fill the entry */
   pEntry->state = DNS_STATE_NEW;
-  pEntry->seqno = dns_seqno++;
+  pEntry->seqno = dns_seqno;
   pEntry->found = found;
   pEntry->arg   = callback_arg;
   namelen = LWIP_MIN(os_strlen(name), DNS_MAX_NAME_LENGTH-1);
   MEMCPY(pEntry->name, name, namelen);
   pEntry->name[namelen] = 0;
 
+  dns_seqno ++;
+  if (dns_seqno == 0xFF) {
+    dns_seqno = 0;
+  }
   /* force to send query without waiting timer */
   dns_check_entry(i);