Gateway MAC address is not used for unicast I/O frames going to devices that are not in the same subnet

In case a unicast connection is opened to a device that is not in the same subnet, the destination MAC address of the I/O frames must be the MAC address of the gateway device.
The current stack uses the broadcast address FF:FF:FF:FF:FF:FF as destination address. This address is limited to the local subnet, so that the I/O frames will not reach the destination device in the other subnet.