OVSDriver: use MAC from getifaddrs if no OVS_VPORT_ATTR_ADDRESS

Reviewer: @rlane

It looks like OpenVSwitch stopped supporting the OVS_VPORT_ATTR_ADDRESS. But, 
IVS seems to depend on that for setting the MAC address of a port and failed. 
This caused the controller to assume the port MAC address to be 
00:00:00:00:00:00 and use that for the LLDP packet-outs. These LLDPs were 
promptly dropped by our Dell switch.