CLEANUP: stream: rename "csf" and "csb" to "scf" and "scb"

These are the stream connectors, let's give them consistent names. The
patch is large (405 locations) but totally trivial.
diff --git a/src/flt_spoe.c b/src/flt_spoe.c
index 88d2d84..c96341d 100644
--- a/src/flt_spoe.c
+++ b/src/flt_spoe.c
@@ -1241,7 +1241,7 @@
 	stream_set_backend(s, agent->b.be);
 
 	/* applet is waiting for data */
-	cs_cant_get(s->csf);
+	cs_cant_get(s->scf);
 
 	s->do_log = NULL;
 	s->res.flags |= CF_READ_DONTWAIT;