almost_full tends to true

The following is only theoretical as I've not checked if it happens or not. But looking at the code and running some simplified computations, I have the impression that the almost_full function may tends to true once the received offset is sufficiently large compared to the initial max_data.

Here, `max_data_next` is increased by the `len` of the emited packets.
https://github.com/cloudflare/quiche/blob/f86de8f18e930f823e00b43b08eee47dc52aa635/src/stream.rs#L872

and `almost_full` is true if `max_data_next/2 > max_data - len` (here, `len` is the total length received).
https://github.com/cloudflare/quiche/blob/f86de8f18e930f823e00b43b08eee47dc52aa635/src/stream.rs#L951

I believe `max_data_next` increases constantly but `max_data - (total)_len` is heuristically bounded by the regular increase of `max_data`. Supposing that this bound is the initial value of `max_data`, then once `max_data_next > 2*initial_max_data` the stream tends to be always declared almost full.

If this is indeed true, the practical implication would be that MAX_STREAM_DATA frames would be send at a high frequency once this threshold is passed. Is it the behavior intended?