Add FIXME memo

Change-Id: I2e1e3159c29f13fb1f61f9bdaba3ba357161edbe
diff --git a/core/api/src/main/java/org/onlab/onos/net/provider/AbstractProviderRegistry.java b/core/api/src/main/java/org/onlab/onos/net/provider/AbstractProviderRegistry.java
index 6cf91a6..a4095ea 100644
--- a/core/api/src/main/java/org/onlab/onos/net/provider/AbstractProviderRegistry.java
+++ b/core/api/src/main/java/org/onlab/onos/net/provider/AbstractProviderRegistry.java
@@ -38,6 +38,7 @@
         S service = createProviderService(provider);
         services.put(provider.id(), service);
         providers.put(provider.id(), provider);
+        // FIXME populate scheme look-up
         return service;
     }