Set the allocator and params on config.
One of allocator and params can be NULL, but not both. When allocator is NULL, the default allocator of the pool will use the values in param to perform its allocation. When param is NULL, the pool will use the provided allocator with its default gstreamer.AllocationParams
A call to Buffer.poolSetConfig can update the allocator and params with the values that it is able to do. Some pools are, for example, not able to operate with different allocators or cannot allocate with the values specified in params. Use Buffer.poolGetConfig to get the currently used values.