mgw: osmo-mgw config should not try to set DSCP > 63

DSCP is a 6-bit value, it cannot be 184.

Change-Id: I9e023125d42ba350c924f2dd7055e84a1a6564cc
diff --git a/mgw/osmo-mgw.cfg b/mgw/osmo-mgw.cfg
index beb6fdf..76525bc 100644
--- a/mgw/osmo-mgw.cfg
+++ b/mgw/osmo-mgw.cfg
@@ -24,7 +24,7 @@
   rtp bind-ip 127.0.0.1
   rtp bind-ip-v6 ::1
   rtp ip-probing
-  rtp ip-dscp 184
+  rtp ip-dscp 46
   no rtp keep-alive
   no rtcp-omit
   no rtp-patch