BUG/MINOR: mux-quic: refactor uni streams TX/send H3 SETTINGS

BUG/MINOR: mux-quic: refactor uni streams TX/send H3 SETTINGS

Remove the unneeded skip over unidirectional streams in qc_send(). This
unify sending for both uni and bidi streams.

In fact, the only local unidirectional streams in use for the moment is
the H3 Control stream responsible of SETTINGS emission. The frame was
already properly generated in qcs.tx.buf, but not send due to stream
skip in qc_send(). Now, there is no need to ignore uni streams so remove
this condition.

This fixes the emission of H3 settings which is now properly emitted.

Uni and bidi streams use the same set of funtcions for sending. One of
the most notable gain is that flow-control is now enforced for uni
streams.