Rebind allowed address pairs only if they changed

This patch ensures allowed address pairs bindings are refreshed
only when they actually change.
This will also avoid sending a notification to the agent if no
change actually occured.

Closes-Bug: #1255145
Partial blueprint neutron-tempest-parallel

Change-Id: Iac2502586a0d215a29194590c16c2e1a064f943b
Merge "Rebind allowed address pairs only if they changed"