CLEANUP: mux-h2: rename all occurrences of stconn "cs" to "sc"

Function arguments and local variables called "cs" were renamed to
"sc" to avoid future confusion. There were also 2 places in traces
where "cs" used to display the stconn, which were turned to "sc".
The "nb_cs" struct field and "h2_has_too_many_cs()" functions were
also renamed.
1 file changed