Coverity warning in XON/XOFF handling

397       /* Adjust the token bucket of this edge connection with the drain rate in
398        * the XON. Rate is in bytes from kilobit (kpbs). */
>>>     CID 1492322:  Integer handling issues  (OVERFLOW_BEFORE_WIDEN)
>>>     Potentially overflowing expression "xon_cell_get_kbps_ewma(xon) * 1000U" with type "unsigned int" (32 bits, unsigned) is evaluated using 32-bit arithmetic, and then used in a context that expects an expression of type "uint64_t" (64 bits, unsigned).
399       uint64_t rate = xon_cell_get_kbps_ewma(xon) * 1000;
400       if (rate == 0 || INT32_MAX < rate) {
401         /* No rate. */
402         rate = INT32_MAX;
403       }
404       token_bucket_rw_adjust(&conn->bucket, (uint32_t) rate, (uint32_t) rate);

cc @dgoulet @mikeperry