Snabb NFV mechanism driver for ML2

Snabb NFV is an open source implementation of Network Functions
Virtualization. http://snabb.co/nfv.html

Change-Id: I2352eca1511e7a7c19ad3261554544ba320d48f0
Implements: blueprint snabb-nfv-mech-driver

Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>