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/peers.c b/src/peers.c
index 8a8e890..649af83 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -1892,7 +1892,7 @@
 		HA_SPIN_UNLOCK(PEER_LOCK, &curpeer->lock);
 	return;
 full:
-	si_applet_cant_put(si);
+	si_cant_put(si);
 	goto out;
 }
 
@@ -1980,7 +1980,7 @@
 	s->flags = SF_ASSIGNED|SF_ADDR_SET;
 
 	/* applet is waiting for data */
-	si_applet_cant_get(&s->si[0]);
+	si_cant_get(&s->si[0]);
 	appctx_wakeup(appctx);
 
 	/* initiate an outgoing connection */