Fix for missing DHCP flow for SR-IOV VMs

Fix for missing DHCP flow for SR-IOV VMs

There is a race condition between NodeListener and
InterfaceListener. It was observed that when new node
got connected, both (NodeListener and InterfaceListener)
events were not handled as tunnel state was unknown.
Hence selection of the designated didn't happen and
DHCP flow was not programmed for SR-IOV VMs.

Fix is made to handle only the InterfaceListener event,
since when node gets connected/disconnected,
we get interface event as well.

Change-Id: I65758220a8d63ad1e91ae38f8895cc10861173ec
Signed-off-by: Ankit Jain <ankit.j.jain@ericsson.com>