QUIC TXP/CHANNEL: Generate MAX_STREAMS using RXFC

QUIC TXP/CHANNEL: Generate MAX_STREAMS using RXFC

Though the RXFC was designed for stream flow control, its logic
is generic enough to use to control MAX_STREAMS generation.

Control of when _we_ can open streams is already done in a bespoke
fashion and doesn't use a TXFC, however (see
ossl_quic_stream_map_update_state).

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20765)