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()
diff --git a/src/dns.c b/src/dns.c
index 69f16bc..749387e 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -764,8 +764,8 @@
 
 	return;
 close:
-	cs_shutw(cs);
-	cs_shutr(cs);
+	sc_shutw(cs);
+	sc_shutr(cs);
 	sc_ic(cs)->flags |= CF_READ_NULL;
 }