mgcp: Honor the rtp IP_TOS settings for Osmux

Honor the IP_TOS settings for Osmux as well. Re-use the RTP
setting as it makes sense to classify the audio packets the
same way.

Fixes: OW#1369
diff --git a/openbsc/src/libmgcp/mgcp_vty.c b/openbsc/src/libmgcp/mgcp_vty.c
index 5124ca6..3d99c83 100644
--- a/openbsc/src/libmgcp/mgcp_vty.c
+++ b/openbsc/src/libmgcp/mgcp_vty.c
@@ -378,7 +378,7 @@
       cfg_mgcp_rtp_ip_dscp_cmd,
       "rtp ip-dscp <0-255>",
       RTP_STR
-      "Apply IP_TOS to the audio stream\n" "The DSCP value\n")
+      "Apply IP_TOS to the audio stream (including Osmux)\n" "The DSCP value\n")
 {
 	int dscp = atoi(argv[0]);
 	g_cfg->endp_dscp = dscp;