BUG/MINOR: stream: bad return code

In error case, we expect the enum ACT_RET_PRS_ERR, but the
function "stream_parse_use_service()" returns "-1"

This patch must be backported in 1.6
diff --git a/src/stream.c b/src/stream.c
index e98ba9f..0d18f9c 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -3302,7 +3302,7 @@
 	/* Check if the service name exists. */
 	if (*(args[*cur_arg]) == 0) {
 		memprintf(err, "'%s' expects a service name.", args[0]);
-		return -1;
+		return ACT_RET_PRS_ERR;
 	}
 
 	/* lookup for keyword corresponding to a service. */