OVN: Add port addresses to IPAM after all ports are joined.

OVN: Add port addresses to IPAM after all ports are joined.

Joining ports involves setting the peer field on ovn_ports. If a switch
port is visited, and it is connected to a router port, then the switch
port's peer is set to the router port and the router port's peer is set
to the switch port.

A router port's addresses are added to IPAM if it is peered with a
switch that has dynamic addressing enabled.

When visiting ports, if a router port is visited before its connected
switch port, then the router port's peer is not set yet. Therefore the
router's port addresses cannot be added to IPAM. The result is that
duplicate addresses can be assigned by a logical switch.

The fix for this is to wait until all ports have been joined and then
add port addresses to IPAM. This way, we guarantee that all peer
assignments have been set, and no duplicate IP addresses may be assigned
by a switch.

Reported-by: James Page <james.page@canonical.com>
Signed-off-by: Mark Michelson <mmichels@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>