Add options to make WAN port Internet State enable or disable

[charithag]

This is adding 2 new functions to Omada class for following:

1. Returns the gateway device specified by the MAC address.
2. Control the internet status of a WAN port in a gateway device specified by the MAC address.

Currently Omada itself does not provide a way to schedule WAN port connectivity. With the given internet-service.py sample, someone can schedule a cron to enable or disable internet access for a given WAN port as required.