ML2 mechanism driver for SR-IOV capable NIC based switching, Part 1

ML2 mechanism driver for SR-IOV capable NIC based switching, Part 1

This set of changes introduces the ML2 mechanism driver for SR-IOV capable NIC based switching.
Please see the blueprint for more information.
The review is submitted in two parts:
- Part 1 (this part)
    The Mechanism Driver to support port binding for SR-IOV virtual functions of
    SRIOV capable switching NICs, such as Mellanox ConnectX Family.

    Use configurable list of supported NIC vendor and product PCI ids to filter
    devices to bind the SR-IOV port.
    Use configurable agent_required option to require SRIOV L2 Agent
    for bort binding.

- Part2
    The SRIOV NIC Based L2 Agent.

Partially implements: blueprint ml2-sriov-nic-switch

Change-Id: If3d28df2a8ffe72ae512ddae076f42fca936cff7