bridge: Remove unwanted ports at time of ofproto creation.

The reconfiguration code only deleted unwanted ports for bridges that had
been created in previous (re)configurations.  In fact, we should run this
step even for bridges that are newly added, e.g. to delete ports that
were added by a previous run of ovs-vswitchd and deleted from the database
between runs.

Before this commit, the following left "int" in datapath br0.  After this
commit, "int" is properly deleted:

1. With ovs-vswitchd running:
      # ovs-vsctl add-br br0
      # ovs-vsctl add-port br0 int -- set interface int type=internal
2. Kill ovs-vswitchd, then:
      # ovs-vsctl --no-wait -- del-port br0 int
3. Restart ovs-vswitchd.

Bug #9957.
Reported-by: Hiroshi Tanaka <htanaka@nicira.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>