There's no need to keep throttle_conflicting(), throttle_is_valid()
and throttle_max_is_missing_limit() as separate functions, so this
patch merges all three into one.

As a consequence, check_throttle_config() becomes redundant and can be
replaced with throttle_is_valid().
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>