ONOS-4801 add default available field to gRPC model

- replace deprecated methods with new Protobuf 3 API
- cosmetic changes

Change-Id: I4655fc0fd76c8de83ea03615fc876c5aa9445367
diff --git a/incubator/protobuf/src/main/proto/Link.proto b/incubator/protobuf/src/main/proto/Link.proto
index b5fcbfc..a1ae8ff 100644
--- a/incubator/protobuf/src/main/proto/Link.proto
+++ b/incubator/protobuf/src/main/proto/Link.proto
@@ -8,7 +8,7 @@
   DIRECT = 0;
 
   // Signifies that this link is potentially comprised from multiple
-  //underlying segments or hops, and as such should be used to tag
+  // underlying segments or hops, and as such should be used to tag
   // links traversing optical paths, tunnels or intervening 'dark'
   // switches.
   INDIRECT = 1;