Close all open connections before reconfiguring the network interface.

When attribute 5 of the TCP/IP is set, the stack will reconfigure the network interface which internally will bring the interface down, reconfigure it and bring it up again.

It is not clear, what happens to the connections which are still open at that point.

For convencience, we should gracefully close all open connections before reconfiguring the network interface, i.e. enqueue a close job for each connection and enqueue the reconfiguration job behind these close jobs.

Also, we should think about a mechanism to prevent the stack from accepting further connections while a reconfiguration of the network interface is ongoing.