Fix problems detected by ErrorProne

Change-Id: I2fc9e3c45bb537fc12aa672fd3ae27423a538b2a
diff --git a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingArpHandler.java b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingArpHandler.java
index 03700cf..4e69759 100644
--- a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingArpHandler.java
+++ b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingArpHandler.java
@@ -637,7 +637,7 @@
                             .stream()
                             .filter(s -> s.getNetworkId().equals(n.getId()))
                             .filter(s -> !Strings.isNullOrEmpty(s.getGateway()))
-                            .filter(s -> !gateways.contains(s.getGateway()))
+                            .filter(s -> !gateways.contains(IpAddress.valueOf(s.getGateway())))
                             .forEach(OpenstackSwitchingArpHandler.this::addSubnetGateway);
                 }
             });