throttle: do not use invalid config in test

The (burst) max parameter cannot be smaller than the avg parameter.
There is a test case that uses avg = 56, max = 1 and gets away with it
because no input validation is performed by the test case.

This patch switches to valid test input parameters.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20170301115026.22621-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>