Make use of Optional more idiomatic

Change-Id: I42b3261169e7cb8408f46c5831f72115f77fd779
diff --git a/app/src/main/java/org/onosproject/olt/impl/Olt.java b/app/src/main/java/org/onosproject/olt/impl/Olt.java
index 16e8a9e..bfc05c8 100644
--- a/app/src/main/java/org/onosproject/olt/impl/Olt.java
+++ b/app/src/main/java/org/onosproject/olt/impl/Olt.java
@@ -256,7 +256,7 @@
         CompletableFuture<ObjectiveError> upFuture = new CompletableFuture();
 
         TrafficSelector upstream = DefaultTrafficSelector.builder()
-                .matchVlanId((defaultVlan.isPresent()) ? defaultVlan.get() : DEFAULT_VLAN)
+                .matchVlanId(defaultVlan.orElse(DEFAULT_VLAN))
                 .matchInPort(subscriberPort)
                 .build();
 
@@ -276,7 +276,7 @@
 
         TrafficTreatment downstreamTreatment = DefaultTrafficTreatment.builder()
                 .popVlan()
-                .setVlanId((defaultVlan.isPresent()) ? defaultVlan.get() : DEFAULT_VLAN)
+                .setVlanId(defaultVlan.orElse(DEFAULT_VLAN))
                 .setOutput(subscriberPort)
                 .build();