Report an error when stork-agent uses interface which is down
As pointed out in the following comment: #395 (comment 160900), it may be desired to report an error when the stork-agent is started with the host
parameter set to the IP address on the non running interface. One way to deal with this would be to refuse starting the stork agent. At very least, the agent should log a warning message and then when the interface is up it should start functioning.