fixes #2010720. This ensures that if the driver has an empty plug/unplug to bond interface function, the code will continue down the old path prior to https://github.com/openstack/networking-generic-switch/commit/aea67080442272e64238fda840bcdeeb5db9ff94 (881945)

fixes #2010720. This ensures that if the driver has an empty plug/unplug to bond interface function, the code will continue down the old path prior to https://github.com/openstack/networking-generic-switch/commit/aea67080442272e64238fda840bcdeeb5db9ff94 (881945) · Gerrit Code Review