handle link commands

def cmd_signing(self, args):
        '''handle link commands'''
        usage = "signing: <setup|remove|disable|key> passphrase"
        if len(args) == 0:
            print(usage)
        elif args[0] == 'setup':
            self.cmd_signing_setup(args[1:])
        elif args[0] == 'key':
            self.cmd_signing_key(args[1:])
        elif args[0] == 'disable':
            self.cmd_signing_disable(args[1:])
        elif args[0] == 'remove':
            self.cmd_signing_remove(args[1:])
        else:
            print(usage)