'Set the default route to go through intf.
intf: Intf or {dev <intfname> via <gw-ip> ...}'

def setDefaultRoute(self, intf=None):

    if (isinstance(intf, basestring) and ('    ' in intf)):
        params = intf
    else:
        params = ('dev    %s' % intf)
    self.cmd('ip    route    del    default;    ip    route    add    default', params)
