connmgr: Suppress duplicate port status notifications.

connmgr: Suppress duplicate port status notifications.

When the status of a port changes, ofproto calls into connmgr to notify
controllers.  Sometimes, particular changes are only visible to controllers
running specific versions of OpenFlow.  Until now, OVS would send those
controllers duplicate port status notifications.  This is unnecessary and
somewhat confusing.  This commit eliminates it.

This commit updates one of the tests not to expect duplicate notifications.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Numan Siddique <nusididq@redhat.com>