Add OVS_DATAPATH_TYPE in portbindings constants
Add OVS_DATAPATH_TYPE in portbindings constants

Added OVS_DATAPATH_TYPE constant in portbindings. This parameter will
be added to OVS backend VIF_DETAILS. This string parameter is used to
define if the bridge uses kernel or userspace datapath.

Change-Id: Ie523c821995c046c7f77783a34e75053fc0abb3d
Related-Bug: #1632372

openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib