The modbus_set_byte_timeout() function shall set the timeout interval between two consecutive bytes of
the same message. The timeout is an upper bound on the amount of time elapsed before select() returns, if
the time elapsed is longer than the defined timeout, an ETIMEDOUT error will be raised by the function
waiting for a response.
The value of to_usec argument must be in the range 0 to 999999.
If both to_sec and to_usec are zero, this timeout will not be used at all. In this case,
modbus_set_response_timeout() governs the entire handling of the response, the full confirmation response
must be received before expiration of the response timeout. When a byte timeout is set, the response
timeout is only used to wait for until the first byte of the response.