CORD-48 Fixing filtering rule bug in multi-instance operation.

Change-Id: Ie91b2efcebff1bdb14357b6720ff8214a712cdc2
diff --git a/src/main/java/org/onosproject/segmentrouting/IcmpHandler.java b/src/main/java/org/onosproject/segmentrouting/IcmpHandler.java
index a77ec95..b3916b0 100644
--- a/src/main/java/org/onosproject/segmentrouting/IcmpHandler.java
+++ b/src/main/java/org/onosproject/segmentrouting/IcmpHandler.java
@@ -32,7 +32,7 @@
 import org.slf4j.LoggerFactory;
 
 import java.nio.ByteBuffer;
-import java.util.List;
+import java.util.Set;
 
 import static com.google.common.base.Preconditions.checkNotNull;
 
@@ -70,7 +70,7 @@
         DeviceId deviceId = connectPoint.deviceId();
         Ip4Address destinationAddress =
                 Ip4Address.valueOf(ipv4.getDestinationAddress());
-        List<Ip4Address> gatewayIpAddresses = config.getPortIPs(deviceId);
+        Set<Ip4Address> gatewayIpAddresses = config.getPortIPs(deviceId);
         Ip4Address routerIp = config.getRouterIp(deviceId);
         IpPrefix routerIpPrefix = IpPrefix.valueOf(routerIp, IpPrefix.MAX_INET_MASK_LENGTH);
         Ip4Address routerIpAddress = routerIpPrefix.getIp4Prefix().address();