Bugfix for github issue 2890.

Changing default behavior of vagrant up to enable "cableconnected" on bridged network devices

plugins/providers/virtualbox/driver/version_4_3.rb

@@ -105,7 +105,7 @@ module VagrantPlugins
 
             if adapter[:bridge]
               args.concat(["--bridgeadapter#{adapter[:adapter]}",
-                          adapter[:bridge]])
+                          adapter[:bridge], "--cableconnected#{adapter[:adapter]}", "on"])
             end
 
             if adapter[:hostonly]