CLEANUP: stconn: rename cs_{shut,chk}* to sc_*

This applies the following renaming:

cs_shutr() -> sc_shutr()
cs_shutw() -> sc_shutw()
cs_chk_rcv() -> sc_chk_rcv()
cs_chk_snd() -> sc_chk_snd()
cs_must_kill_conn() -> sc_must_kill_conn()
18 files changed