Workaround: add default dpopts='--no-slicing' to UserSwitch

This disables slicing by default but fixes bandwidth limits.
Eventually we want to enable both to work together, but for now
this enables one or the other depending on the dpopts setting.

mininet/node.py

@@ -801,9 +801,10 @@ class UserSwitch( Switch ):
 
     dpidLen = 12
 
-    def __init__( self, name, dpopts='', **kwargs ):
+    def __init__( self, name, dpopts='--no-slicing', **kwargs ):
         """Init.
-           name: name for the switch"""
+           name: name for the switch
+           dpopts: additional arguments to ofdatapath (--no-slicing)"""
         Switch.__init__( self, name, **kwargs )
         pathCheck( 'ofdatapath', 'ofprotocol',
                    moduleName='the OpenFlow reference user switch' +