be2net driver : emit a message on ifdown

Issue

• If a cable is pulled from an be2net NIC, the syslog receives a "Link down" message. But if an ifdown is performed on the same be2net NIC, there is no message.
• My customer has an existing code-base developed on another operating system. Their opinion is that all loss of carrier and / or link should be logged, regardless of the reason why the loss occurred. They say, and I agree, that this is an OS feature, not something that they should be required to invest in, and implement in their code.