fix kwargs names so they wont spark a warning

examples/controlnet.py

@@ -100,7 +100,7 @@ class MininetFacade( object ):
 
 class ControlNetwork( Topo ):
     "Control Network Topology"
-    def build( self, n, dataController=DataController, **kwargs ):
+    def build( self, n, dataController=DataController, **_kwargs ):
         """n: number of data network controller nodes
            dataController: class for data network controllers"""
         # Connect everything to a single switch

examples/multilink.py

@@ -21,7 +21,7 @@ def runMultiLink():
 class simpleMultiLinkTopo( Topo ):
     "Simple topology with multiple links"
 
-    def build( self, n, **kwargs ):
+    def build( self, n, **_kwargs ):
         h1, h2 = self.addHost( 'h1' ), self.addHost( 'h2' )
         s1 = self.addSwitch( 's1' )
 

examples/natnet.py

@@ -27,7 +27,7 @@ from mininet.util import irange
 
 class InternetTopo(Topo):
     "Single switch connected to n hosts."
-    def build(self, n=2, **opts):
+    def build(self, n=2, **_kwargs ):
         # set up inet switch
         inetSwitch = self.addSwitch('s0')
         # add inet host