Want to fix "ethmonitor does not return the correct link status"

The function get_link_status in ethmonitor does not return the correct link status in the following scenarios:
1). when the wire is unplugged from network interface
eth0: mtu 1500 qdisc mq state DOWN qlen 1000
2). when lower layer is down for a VLAN
vlan2@bond0: mtu 1500 qdisc noqueue state LOWERLAYERDOWN

Fix the issue NO.#235: https://github.com/ClusterLabs/resource-agents/issues/235