ML2: Make get_device_details report mac address as well

This will be used by ofagent to route packets to local VMs.

Partially-implements: blueprint ofagent-merge-bridges
Change-Id: Icaa26448a370dd75d09e95ed439df5b486a862cf
l2pop: get_agent_ports: Don't yield (None, {})

There's no point to yield None lvm with empty entries.

Closes-Bug: #1355759
Related: blueprint ofagent-l2pop
Change-Id: I42aeb48a062d35038116978d70c8dac4139a5583
Merge "ML2: Make get_device_details report mac address as well"
Merge "l2pop: get_agent_ports: Don't yield (None, {})"