MINOR: stream-int: rename si_applet_{want|stop|cant}_{get|put}

It doesn't make sense to limit this code to applets, as any stream
interface can use it. Let's rename it by simply dropping the "applet_"
part of the name. No other change was made except updating the comments.
diff --git a/src/cache.c b/src/cache.c
index 96a251a..6988b15 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -617,7 +617,7 @@
 			offset = 0;
 		if (ret <= 0) {
 			if (ret == -3 || ret == -1) {
-				si_applet_cant_put(si);
+				si_cant_put(si);
 				break;
 			}
 			return -1;
@@ -644,7 +644,7 @@
 
 	/* Check if the input buffer is avalaible. */
 	if (res->buf.size == 0) {
-		si_applet_cant_put(si);
+		si_cant_put(si);
 		goto out;
 	}
 
@@ -1140,7 +1140,7 @@
 		if (!next_key) {
 			chunk_printf(&trash, "%p: %s (shctx:%p, available blocks:%d)\n", cache, cache->id, shctx_ptr(cache), shctx_ptr(cache)->nbav);
 			if (ci_putchk(si_ic(si), &trash) == -1) {
-				si_applet_cant_put(si);
+				si_cant_put(si);
 				return 0;
 			}
 		}
@@ -1166,7 +1166,7 @@
 			shctx_unlock(shctx_ptr(cache));
 
 			if (ci_putchk(si_ic(si), &trash) == -1) {
-				si_applet_cant_put(si);
+				si_cant_put(si);
 				return 0;
 			}
 		}