Gateway mac table should have unique MAC address for vhu hosts other than 00:00:00...

Gateway mac table should have unique MAC address for vhu hosts other than 00:00:00:00:00:00

Description : With OVS DPDK ports, the port physical address is always coming as "00:00:00:00:00:00".
Because of this interface-manager stores the phyaddress of all interfaces on top of this port
as "00:00:00:00:00:00", there by responding to the ARP requests with this MAC address for
netvirt L3VPN usecases.
For address this issue, whenever an openflow port added notification comes with hardware address "00:00:00:00:00:00",
a mac address is generated for the same using its port-number and de:ad:be:ef prefix,
and this generated mac-address will be used in all subsequent processing.

Change-Id: I305288e44d12993f8f1bad9932c19ca86fa6afca
Signed-off-by: Faseela K <faseela.k@ericsson.com>