unbreak C89

mongoose.c

@@ -19287,6 +19287,15 @@ uint64_t mg_millis(void) {
 }
 #endif
 
+// network format equates big endian order
+uint16_t mg_ntohs(uint16_t net) {
+  return MG_LOAD_BE16(&net);
+}
+
+uint32_t mg_ntohl(uint32_t net) {
+  return MG_LOAD_BE32(&net);
+}
+
 #ifdef MG_ENABLE_LINES
 #line 1 "src/wifi_dummy.c"
 #endif