Make use of one instance of IPDB
Make use of one instance of IPDB

Creating an instance of IPDB for each use of binding, has a
significant impact on the scalability of Kuryr. As the number of
containers on a host increases, the cost of attaching a container to a
network increases rapidly. This patch, fixes the problem.

Change-Id: Id7dff9348acd36481146e4edfba8f92cff040ced
Closes-Bug: #1539252

celebdor/kuryr-libnetwork,celebdor/kuryr-libnetwork,midonet/kuryr,openstack/kuryr,celebdor/kuryr,midonet/kuryr,celebdor/kuryr-libnetwork,celebdor/kuryr,openstack/kuryr,midonet/kuryr