MINOR: mux_quic: remove duplicate QMux local transport params

MINOR: mux_quic: remove duplicate QMux local transport params

When QMux was first implemented, values used for emitted transport
parameters in xprt_qstrm and local flow control in mux_quic were
initialized separately. This is error prone in particular if a value is
change in one layer but not the other.

This patch fixes this by using xprt_qstrm_lparams() in QMux init
function. Mux flow control is then loaded with these values. Thus all
values are now initialized in a single place which is xprt_qstrm_init().