consume neutron-lib callbacks
consume neutron-lib callbacks

The callback system in neutron has moved to neutron-lib and hence
consumers need to follow suit.
See Ib6baee2aaeb044aaba42a97b35900d75dd43021f for more details.

Change-Id: I87ddfb13a84147acf4f9ca68d86fc6112bf7859b

openstack/networking-bagpipe-l2,openstack/networking-bagpipe-l2,stackforge/networking-bagpipe-l2,openstack/networking-bagpipe,stackforge/networking-bagpipe-l2,openstack/networking-bagpipe