Fixed issue with pushing topo JSON after devices are in the system.

Fixes ONOS-2463.

Ported from onos-1.2 branch.

Change-Id: I9ce7a11e50d8fd6c344be2f90dc046dcba65fe46
(cherry picked from commit 914c3521)

@@ -447,6 +447,7 @@ class ConfigProvider implements DeviceProvider, LinkProvider, HostProvider {
 
     // Adds any missing device ports.
     private void addMissingPorts(Device device) {
+        try {
             List<Port> ports = deviceService.getPorts(device.id());
             Set<ConnectPoint> existing = ports.stream()
                     .map(p -> new ConnectPoint(device.id(), p.number()))
@@ -456,12 +457,17 @@ class ConfigProvider implements DeviceProvider, LinkProvider, HostProvider {
                     .filter(cp -> !existing.contains(cp))
                     .collect(Collectors.toSet());
 
+            if (!missing.isEmpty()) {
                 List<PortDescription> newPorts = Stream.concat(
                         ports.stream().map(this::description),
                         missing.stream().map(this::description)
                 ).collect(Collectors.toList());
                 deviceProviderService.updatePorts(device.id(), newPorts);
             }
+        } catch (IllegalArgumentException e) {
+            log.warn("Error pushing ports: {}", e.getMessage());
+        }
+    }
 
     // Creates a port description from the specified port.
     private PortDescription description(Port p) {