[ONOS-4520] Separate model messages from service messages in ProtoBuf IDL.

- move ProtoBuf generated code in a package similar to ONOS models.

Change-Id: I5deb591094c2b8af2b22041da935567fc8dacd87
diff --git a/incubator/rpc-grpc/src/main/proto/LinkService.proto b/incubator/rpc-grpc/src/main/proto/LinkService.proto
new file mode 100644
index 0000000..99e0f22
--- /dev/null
+++ b/incubator/rpc-grpc/src/main/proto/LinkService.proto
@@ -0,0 +1,30 @@
+syntax = "proto3";
+option java_package = "org.onosproject.grpc.net.link";
+
+import "Link.proto";
+
+package Link;
+
+// Message to represent no return value
+message Void {}
+
+message LinkDetectedMsg {
+  // ProviderId scheme only
+  string provider_id = 1;
+  LinkDescription link_description = 2;
+}
+
+message LinkVanishedMsg {
+  // ProviderId scheme only
+  string provider_id = 1;
+  oneof subject {
+    LinkDescription link_description = 2;
+    ConnectPoint connect_point = 3;
+    string device_id = 4;
+  }
+}
+
+service LinkProviderServiceRpc {
+  rpc LinkDetected(LinkDetectedMsg) returns (Void);
+  rpc LinkVanished(LinkVanishedMsg) returns (Void);
+}