Ignore double messages to associate the same ip

Associating an ip removes the old association and adds a new one.
If we are already associated to the target ip, then we can avoid
sending extra messages and making db calls. The current possibility
of a double send contributes to bug 1092762.

Change-Id: I5a40177fcd05b150f39e3144c1d521bd979b358b
Merge "Ignore double messages to associate the same ip"