extmod/modlwip: lwip_tcp_receive: Properly map lwIP error to POSIX errno.

extmod/modlwip.c

@@ -396,7 +396,8 @@ STATIC mp_uint_t lwip_tcp_receive(lwip_socket_obj_t *socket, byte *buf, mp_uint_
                 return 0;
             }
         } else if (socket->state != STATE_CONNECTED) {
-            *_errno = -socket->state;
+            assert(socket->state < 0);
+            *_errno = error_lookup_table[-socket->state];
             return -1;
         }
     }