GossipLinkStore: removedLinks could be accessed concurrently by advertisement

Change-Id: I64cc3c5614182b6d6a8c2bf1dfa99e3f25fb9817
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/link/impl/GossipLinkStore.java b/core/store/dist/src/main/java/org/onlab/onos/store/link/impl/GossipLinkStore.java
index 2a60120..0332a7e 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/link/impl/GossipLinkStore.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/link/impl/GossipLinkStore.java
@@ -19,7 +19,6 @@
 import com.google.common.collect.FluentIterable;
 import com.google.common.collect.HashMultimap;
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.Maps;
 import com.google.common.collect.SetMultimap;
 
 import org.apache.commons.lang3.RandomUtils;
@@ -118,7 +117,7 @@
     private final SetMultimap<DeviceId, LinkKey> dstLinks = createSynchronizedHashMultiMap();
 
     // Remove links
-    private final Map<LinkKey, Timestamp> removedLinks = Maps.newHashMap();
+    private final Map<LinkKey, Timestamp> removedLinks = new ConcurrentHashMap<>();
 
     @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
     protected DeviceClockService deviceClockService;