osmux: osmux batch-factor can't be higher than 8

The osmux header uses a counter of 3 bits, so you can put up to
8 message in it.

openbsc/src/libmgcp/mgcp_vty.c

@@ -1130,7 +1130,7 @@ DEFUN(cfg_mgcp_osmux,
 
 DEFUN(cfg_mgcp_osmux_batch_factor,
       cfg_mgcp_osmux_batch_factor_cmd,
-      "osmux batch-factor <1-16>",
+      "osmux batch-factor <1-8>",
       OSMUX_STR "Batching factor\n" "Number of messages in the batch\n")
 {
 	g_cfg->osmux_batch = atoi(argv[0]);