Override modify to check kwargs before request sent to device.

def _modify(self, **patch):
        """Override modify to check kwargs before request sent to device."""
        if 'state' in patch:
            if patch['state'] != 'user-up' and patch['state'] != 'user-down':
                msg = "The members resource does not support a modify with " \
                      "the value of the 'state' attribute as %s. " \
                      "The accepted values are 'user-up' or " \
                      "'user-down'" % patch['state']
                raise MemberStateModifyUnsupported(msg)
        if 'session' in patch:
            if patch['session'] != 'user-enabled' and patch['session'] != \
                    'user-disabled':
                msg = "The members resource does not support a modify with " \
                      "the value of the 'session' attribute as %s. " \
                      "The accepted values are 'user-enabled' or " \
                      "'user-disabled'" % patch['session']
                raise MemberStateModifyUnsupported(msg)
        super(Members, self)._modify(**patch)