fix tcp_pseudo_checksum: add ntohs() to correctly extract 16-bit IP halfwords from NBO on LE

src/lwip_tcp/lwip_tcp_out.c

@@ -596,10 +596,10 @@ tcp_pseudo_checksum(uint32_t src_ip, uint32_t dst_ip, uint8_t proto, uint16_t tc
 {
     uint32_t sum = 0;
 
-    sum += (uint32_t)(uint16_t)((src_ip >> 16) & 0xFFFF);
-    sum += (uint32_t)(uint16_t)(src_ip & 0xFFFF);
-    sum += (uint32_t)(uint16_t)((dst_ip >> 16) & 0xFFFF);
-    sum += (uint32_t)(uint16_t)(dst_ip & 0xFFFF);
+    sum += (uint32_t)ntohs((uint16_t)((src_ip >> 16) & 0xFFFF));
+    sum += (uint32_t)ntohs((uint16_t)(src_ip & 0xFFFF));
+    sum += (uint32_t)ntohs((uint16_t)((dst_ip >> 16) & 0xFFFF));
+    sum += (uint32_t)ntohs((uint16_t)(dst_ip & 0xFFFF));
     sum += htons((uint16_t)proto);
     sum += htons(tcp_len);