Zabbix: Monitor PoE on RouterBOARD devices

Some RouterBOARD devices (those with “P” in the model name) have the ability to power devices through Power-over-Ethernet (PoE for short). It is a very useful thing, especially after the PoE firmware upgrade to the latest version (currently 2.1), which increases the current limit for the device and port, adds support for port priority and especially allows monitoring voltage, current and power of the connected device.