Change default --listenport to 6654

Previously the standard OpenFlow poort (6653) that Controller()
may be listening at would conflict with the default listenPort
for switch 20 (usually UserSwitch 20), breaking waitConnected()
and disconnecting that switch from the network in general.

Fixes #668

bin/mn

@@ -257,7 +257,7 @@ class MininetRunner( object ):
                          help = '|'.join( LEVELS.keys() )  )
         opts.add_option( '--innamespace', action='store_true',
                          default=False, help='sw and ctrl in namespace?' )
-        opts.add_option( '--listenport', type='int', default=6634,
+        opts.add_option( '--listenport', type='int', default=6654,
                          help='base port for passive switch listening' )
         opts.add_option( '--nolistenport', action='store_true',
                          default=False, help="don't use passive listening " +