Add temporary solution in order to support multiple physical networks
by mlnx ML2 MechanismDriver.
Due to non merged patches in nova that should support propagating
physical_network retrieved from port binding:profile attribute
to VIF/Network object.
The code will be removed once relevant nova patches are merged.
The code is disabled by default and should be enabled via
ml2_conf_mlnx.ini config file.
Change-Id: I815f9e28774efd47bccd1c57481e6ba89075792b
Closes-bug: #1291209
4a3a1bd2a2