ONOS-4646: Provide temp. mechanism for topology overlays to modify link details data.

Change-Id: I00b78b1da1580883e09af87ed470e6142a1ec19b
(cherry picked from commit 4f732d2)
diff --git a/web/gui/src/main/webapp/app/view/topo/topoModel.js b/web/gui/src/main/webapp/app/view/topo/topoModel.js
index d8f279b..d104449 100644
--- a/web/gui/src/main/webapp/app/view/topo/topoModel.js
+++ b/web/gui/src/main/webapp/app/view/topo/topoModel.js
@@ -230,7 +230,8 @@
                     ws = (s && s.linkWidth) || 0,
                     wt = (t && t.linkWidth) || 0;
                 return lnk.position.multiLink ? 5 : Math.max(ws, wt);
-            }
+            },
+            extra: link.extra
         });
         return lnk;
     }